Over the weekend, I took over a dozen games to GameStop and sold them. Got some reasonable credit for them towards buying stuff there. The question then comes up: what games to sell off? What games to keep?
It's all based on replayability. I sold off the games that I knew that I wouldn't play any more. Generally, the games that I have finished, tho there were a couple where I never finished it but a sequal is out already (e.g. sold Tony Hawk Pro Skate 4 cuz I also have THPS: Underground).
What makes a game replayable? A number of factors: are there other modes you can try? If you play it again, do you have choices that will change the gameplay or the story? Are there multiple paths and strategies towards finishing the game? Is it something that you might play with friends?
One game that I love, but sold off was D&D: Heroes. I played through it as a fighter (surprise, surprise), so I could play it again as (say) a mage. But the story line and the exploration and the puzzles will be unchanged. I'll get to see and use some spells and some minor strategy variants for using a mage. But the bulk of the game (about 25 hours of play) will be just the same. D&D: Heroes is also a fantastic game for a group of (up to) four people. But it isn't something you just sit down and play with a friend one evening. Even at four hours a night, you'll play it for a week. That's pretty hard to get into. If it was online, then that might be a bit different. But, sadly, the game is not Xbox Live-capable.
Now, on the other hand, I've basically finished Burnout 3: Takedown. But I'm not going to sell that unless/until Burnout 4 comes out. Why? It's a game where you can just sit down and have fun with it. No investment. No length brain-engagement. And it is fantastic for a quick play with friends. Same kind of thing with Timesplitters 3.
When buying a game, consider its potential for replayability. Something like Dynasty Warriors has been a fantastic buy for me. I can just keep going back to play through campaigns with new characters. It is a little repetitive, but as I've said here before: it can be a fantastic game when you're up for some hack and slash.
RPGs will generally not be replayable, though the developers are trying to make them so. Two recent games, Knights of the Old Republic (KOTOR) and Fable, have a good or evil decision that you can make. But you have to ask: will the game be that different if I play the other alignment? I believe the answer is "no", so I'm not going to be replaying Fable as an evil guy. Might be fun, sure, but worth another 25 or 30 hours? Probably not.
This is a big topic, so I'll stop now and hopefully revisit on another day...