I started going back in 1985 and while not making every Gen Con have been to about 25 of them, some have been great, and some have been just okay, but I have never been disappointed.
People will say it is too crowded and talk about getting a close hotel, but that has always been an issue.
Hotels have always been an issue, but the crowding is definitely new. I also have been going since Milwaukee days and the last five years or so have seen substantial changes that have led to me being less interested in Gen Con nowadays. Specifically:
Fewer Exciting Cool New Things
Obviously not specific to GenCon, but Gen Con was the place people used to release their new and cool product. Now it's on Kickstarter, more likely. I remember dashing off to my favorite companies to see what was new and exciting. Now, at best, I go to pick up my KS rewards from them. So the dealer hall experience is less exciting, and more of a search for things that went under my radar. Still fun, but a change from "WOW" to "nice".
Crowds
Maybe 5 years ago at the last Gen Con I went to, I made the mistake of trying to cross across the center near the dealer hall area as it was opening and it took my 20 minutes of being packed into a crowd. Covid or no Covid, that's just no fun. If you are short, you will see a lot of people's backs at GenCon
Game Variety
For GenCon I always look through the list of games on the search for smaller games and systems that I'd like to try out and see how they play. But recently they have been very hard to find. Looking through the list of games on offer, it's hard to find even relatively well-known smaller games. I used to look for the latest Paranoia, Godlike, One Ring, etc offerings -- but they are much rarer than they used to be. Maybe a lot of potential GMs have been put off by the following issue:
Ghosting Games
With the broadening of appeal of games (a good thing!) Gen Con now has a lot of people who are gently committed fans; not as "core gamer" as in previous years. This is a great thing for the hobby, but on a personal level it makes GenCon less fun. It used to be that if you ran a game, or played in one, you would be 90% sure that everyone would turn up. I recall in Milwaukee at the Cthulhu Masters that waiting for half an hour before a game so that you would be the earliest of the alternates if someone dropped was almost expected. Nowadays I pretty much expect that up to half the people simply won't show because they double-booked, or were having a fun conversation, or so on. It's particularly bad at GenCon because the total cost is so high, that the financial cost of missing a game is effectively zero. You might as well buy tickets for every possible hour of the day and then just go to ones as the day turns out. For smaller cons, I find this is is not the case -- perhaps because there's less to do than actually game!
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Overall, GenCon doesn't feel like "The Best Four Days in Gaming" anymore -- it feels like "The Best Four Days in Gaming Culture". It's a great place to hang with friends, experience the community and wander around seeing what people are into. But for actually playing games -- which is really why I go to cons -- it's a poor return on time and money. So if you want the experience of Gaming Culture, or if you've never been to Gen Con before, absolutely go for it! But if you actually want to play games, maybe look elsewhere.