If you liked GTA you should for sure get Red Dead. I know that Future Shop and Best Buy in my area have been doing a deal where you could trade 2 games in that are worth at least $5 and get Red Dead free so you could see if any of the Future Shop's or Best Buy's are doing that and save yourself some money.
Dead Space can be bought used for like $15 if you want that. It has a demo on the XBL Marketplace. I think the demo is quite different than the full game though. If you like a little creepiness and a good story though I would recommend Dead Space like I said.
I saw that you were looking for other games to try because you mostly play Halo and CoD.
Try Dead Space. It isn't much like either of them but once you get the controls it is a really great game. Just rent it though. It's a creepy game with a great story. Too bad there is no multiplayer.
If you're looking for multiplayer though try Red Dead. I just got it the Free Roam multiplayer is hella fun. I played for 7 hours straight with a few friends the night I got it and I didn't get bored. I just got tired.
Also are you on XForgery? I think I've seen your name before. Like 95% sure.