Homefront has a very short single player campaign, I ran through it in about 4 hours. It's your standard generic shooter, not all that great. I'm not sure how well populated the multiplayer is for Homefront these days, but if you aren't planning on doing a lot of multiplayer, best to just rent Homefront, you could easily run through it in an afternoon.
Crysis 2 I haven't played, but the general consensus from reviews is it is a much better game, I believe its single player campaign runs about 8 hours. The Xbox 360 does struggle with Crysis 2 though, be prepared for the framerate to drop below 30FPS when things get busy on screen.