As a kid I attended several gaming conventions - my home-town sponsored two (Glathricon, an all-gaming con, in the summer, and ConTact, a more traditional SF con with a large gaming component, in the fall) that I went to starting in the fall of '86 until the sort of withered away in the early 90s, and starting in 1988 I also attended GenCon every year through 1997 (the summer after I graduated college; right before I moved permanently to the other side of the country). At those conventions I played a lot of games, both rpgs and more traditional boardgames, minis games, etc. By and large, and certainly with some notable exceptions, most of the rpg games weren't very good.
Part of it is that a big element of the appeal in rpgs is the open-ended campaign structure - maintaining the same character through a series of adventures, watching him or her become more powerful and develop more of an individual personality, learning more about the world, developing friends and enemies (players and NPCs alike), becoming involved in long-term plots that might play out slowly over months or years, and so on. Another big element of the appeal of rpgs is that they're a social game played with a group of friends, and in many play-sessions as much or more of the fun comes from the social interaction between the players than the ostensible action of the game. As a kid I thought you were supposed to resist that - to keep the action focused in-game and avoid distractions and digressions - but playing with Gary Gygax taught me it's closer to the opposite.
At a convention, where you've got a single 4-hour block of time and are likely playing with a group of mostly strangers, both of those are eliminated, so a convention game is necessarily going to be a different sort of beast than a game at home with your buddies. The earliest convention games of D&D seem to have been, effectively, demonstrations - you'd sit down for a couple of hours and do some exploring inside Greyhawk Castle or the Sunken City of Kalibruhn or wherever, and hopefully would have a good enough time that you'd be inspired to pick of a copy of the rules and take them home and start your own campaign. Gary Gygax came up with a different idea for the first Origins convention - a tournament where various teams went into Gary's almost-cartoonishly-deadly "Tomb of Horrors" (originally devised as Gary's way of testing the skill and mettle of overly-confident players) and the group that made it the furthest before dying was the winner. This formula was refined over the next few years and eventually became what we see in published AD&D modules derived from tournaments like C1, C2, and the A-series: teams of players go through the same adventure, facing the same encounters, and a score is kept with a basic formula of how many encounters were completed graphed to how many characters survived plus bonus points or penalties for particular smart (or dumb) actions. As the tournaments got bigger, they began to have multiple rounds, where the teams that scored best in the first round advanced to the second round (usually a more difficult set of encounters), those who scored best in the second round advanced to the finals (usually something completely off-the-wall), and the team that scored best in the final round was the winner.
That's a mutated form of D&D that doesn't have a lot in common with the default campaign style of play (strategies that are successful in one will lead to failure in the other, and vice versa), but it's still fun in its own way: knowing that the clock is ticking, and that your group's performance is being judged against other groups, puts a lot of pressure on and leads to some really intense and exhilarating play. I played in a couple of tournaments that were run this way (the AD&D Open at GenCon continued to function in this manner even after other tournaments didn't) and although I never did very well, because I was always teamed with strangers, and these adventures placed a very high premium on effective teamwork, I always had fun.
Sadly (from my perspective), when Frank Mentzer founded the RPGA (RolePlaying Game Association, an organization run by TSR with the mandate "to promote quality roleplaying and bring fans of roleplaying games together") in 1981, the way D&D tournaments were organized and scored changed dramatically. Instead of team vs. team, advancement (and, in the final round, winners) were determined individually, based on a vote by the other players (and possibly the DM - I can no longer remember whether the DM got a full vote or was only a tiebreaker) at the end of the session. Along with this, the RPGA introduced an "XP" system for its members where the more tournaments you played in and the better you placed the more points you earned, and as you increased in "level" you got to play in Master-only (and, eventually Grand Master-only) tournaments. This had an obvious and profound (and possibly unintentional?) effect on how tournament play worked. For one thing, teamwork no longer mattered, and neither did process through the adventure. The only thing that mattered was how much you impressed the other players. Maybe they'd be impressed by your tactical acumen and rules-knowledge and effective leadership (and that's what the early RPGA tournaments seem to have expected, because structurally they're still very similar to the pre-RPGA tournaments - linear gauntlets of puzzles and combat), but way more often the vote went to the "best roleplayer" - the hammy actors and scene-stealers. This created a spiral of perverse incentives where players would attempt to out-ham each other, and the adventure itself became mostly irrelevant, until the writers caught on and changed the nature of the adventures to become, basically, just a series of role-playing cues.
I was shy and socially-awkward as a kid, especially around strangers and older people (which meant pretty much everybody at cons). Therefore, I tended to do really badly in these games and rarely advanced beyond the first round. I suppose the idea was that shy kids would be drawn out and feel comfortable enough to participate, but for me it was more the opposite - the more emotive and hammy the other players got, the more I was likely to clam up. This was frustrating in a number of ways: one is that it wasn't much fun for me, another is that it suggested I wasn't actually very good at my favorite game that I'd been totally obsessed with for several years, and called into question whether I'd even really understood the game, because the way it was played in RPGA events was very different than what I'd imagined from reading the books or how we always played at home. This is about the time I probably should have decided the game wasn't really for me after all and declare that I'd "outgrown" it, which is what most other kids did (and, non-coincidentally this was right at the time, in the late 80s, when the fad years were over and the popularity of the game was in steep decline), but for whatever reason I didn't - I kept going to the cons and playing in tournament events that I didn't really enjoy and wasn't very good at. I suppose I was still hoping if I played in enough I might finally find a good one.
And that is, of course, exactly what happened when I lucked into those games with Gary at Glathricon '88. This, finally, was exactly what I'd always wanted D&D to be (and more). It was both a revelation (that my approach to D&D was much closer to how the inventor of the game did it than how everyone else did) and a huge confidence-booster (I was now assured that my approach was "right" after all). I hadn't seen it at the time, but years later I stumbled across a Dragon editorial by Gary (in issue #102, October 1985 - coincidentally one of his last editorials before his ouster) where he expressed the same sentiments - decrying "the current vogue of placing seemingly undue importance" on the "theatrical side of gaming," which he felt "tend[ed] to make
playing out an adventure more of a childrens 'lets pretend' activity than an
action-packed game which involves all sorts
of fun, including the playing of a role but
other fun aspects as well." My approach to gaming was out of fashion in the late 80s, but at least I had the inventor of the game in my corner :)
I still played in a few more RPGA tournaments (in retrospect I'm not sure why - inertia?) but came to realize that those were the least fun games, and that it was much more fun (and instructional) to play in games that went all the way back to the original model - creators of the game giving, basically, demonstrations. That's effectively what the Gygax games had been, and I had similarly fun experiences playing games like Cyberpunk, MegaTraveller, RuneQuest, and Amber at GenCon with "insiders" - not usually the creator of the game, but friends of the creator who'd played with them and been involved in the development and had a "feel" for the game that only comes from that sort of close, long-term association. I almost always came away from those games excited and enthused, eager to share the experience with all of my friends at home (and it's no coincidence that those are the games we played most through the late 80s & 90s). I think there's really something to playing a game with the creator, or someone closely associated with and who learned from the creator, that helps you understand and appreciate it in a way that reading the books alone can never do.
Eventually, for whatever reason - because I wasn't as interested in the new games being released, or felt I'd learned enough, or just realized that playing games with strangers that weren't as good as what I could play at home with my friends wasn't an effective use of my time, I stopped playing even in those demo-games, and the last 3-4 years I attended GenCon, and the last year or two I attended Glathricon, I didn't play in any rpg events, RPGA-sponsored or otherwise. Instead, I realized that the most fun was to be had in large-scale, multiplayer board and minis games. At Glathricon for several years running, a guy named Greg Poehlein (who was one of Evansville's local rpg-industry celebrities, having co-written the Star Trek and Doctor Who rpgs for FASA) ran an event called the "Glathricon 500," which was his house-ruled adaptation of Avalon Hill's Speed Circuit for Matchbox cars on a huge oval-shaped track. This was an all-day event that usually drew around 20 players. Likewise, there was a group who every year at GenCon staged huge 25mm-scale British colonial minis games, with full terrain and hundreds of figures per side (the two I remember were vs. Zulus and vs. Afghans) - again, an all-day event with a dozen or more players involved. These were things I'd never have had the resources or the number of players (or the space!) to attempt at home, and they were always tremendous fun and I looked forward to them year after year (and was crushed when I attended Glathricon '95 and found that "the 500" had been canceled).
Is there a point in all of this? Not really; it's just a reminiscence. But there are, perhaps, a few takeaways that might be useful to people attending, or thinking of attending, a gaming con: (1) the games aren't going to be much like, and probably won't be as good as, your games with your friends at home; (2) tournament-games are especially wack, unless it's a team-tournament and you're there with enough of your home-group to make up a whole team; but (3) if you get a chance to play a game with its creator it's probably worth doing because you'll likely pick up some insight into the expected play-style and get a better feel for the game than you can get from reading a rulebook; and (4) if they're running any large-scale, multiplayer board or minis events, jump all over that, because that's something you can't do at home, and they tend to be really fun!