Hmm. Forza 3 is great and most likely Forza 4 will be too. If you like sim racing games. I fancy Forza 3 more than Gran Turismo 5 in that aspect. Though it does get quite boring after a while. You can pick up the ultimate edition with every bonus car pack for $30 at the moment. Mass Effect moved to PS 3 I thought so isn't an exclusive anymore, but they're decent games. Halo is good, if you can get it for $20. But I don't enjoy the multiplayer as much as CoD or Battlfield. Crackdown 2 was okay but I got bored of it pretty fast. The multiplayer was interesting as well, so if you can get it cheap (10-15$ used most likely) it would be worth it. Haven't played the first one.
I like Forza but Forza 4( I think ) has the lexus LFA in it and I LOVE that car. So I will be getting it. The only sim racing game I've owned is GT 3 and I hated it. I think my hate for it came from when i was in 3rd grade and for christmas we got a ps2 and it came with some Monster truck game and GT3, and I thought GT3 was Grand theft auto 3, which was a game I really wanted for it. So I put it in to play and it was a boring racing game. I think I'll like forza alot better before of the customization I can do to the cars(and more realistic damage system) and I believe you move up faster through Forza than you can through gt, it took FOREVER for me just to get my 2nd car on that game. And I hate crackdown its hard to look at. Battlefield and COD are fun. But CoD is my filler game series. Like when I don't have a really good game to play, I just get on MP on Black ops, the campaign is not that fun b/c the a.i. teammates either make you do all the work or do all the work for you.