Absolutely worth it to me. It's not very good if you're one of those people who have to play new games right away as it can take 6 months or more after release to get a popular game.
But I'm always a good bit behind on gaming anyway (playing Assassin's Creed 2 now, Fallout 3 up next) so it's great for me.
It's super easy since the system is totally automated so you don't have the communication hassles you get with eBay or Craigslist or Amazon.
Point values for games are pretty good--it's probably not for the cheapasses who want to get the most value out of everything they sell/trade. So eBay or Craigslist is probably the way to go if you want to maximize what you get out of every game.
But for me, I don't mind the wait, don't care if I get max value (just don't want ripped off like Gamestops trade in values), and I'm busy as hell so Goozex is great for me since it's so easy to use. Just list games to offer and request, and do nothing until you get matched up. Then print out a shipping label and send it out.
Not for everyone, but I've loved the service the year and a half or so I've been using. I've never been a collector or one to replay games, so I love having such an easy way to get rid of games after beating them, and I've gotten all but 2 of my games over the past 18 months or so from them. Only games I've bought new the past couple of years were Gears 2 and MW2. Everything else I just wait for Goozex.
But again if you mind the wait, want cash instead of points, want to maximize your sales etc., then it's probably not worth it. If you want a super convenient way to just get rid of your games, and get a lot more for them than you will from Gamestop, then it's very much worth it. I care more about convenience than anything else--a lot of the games I've traded would have probably just ended up donated vs. sold in the past.
