Game recommendations for 360?

Hey guys, first post in the Gaming forum. I just got an Xbox 360 for Christmas, and it's really my first console (if you don't count the original Xbox I had about four years ago, and which died after a year.)

I'm relatively new to gaming, and would love some recommendations for some great games for the 360. So far I have Tomb Raider - which I'm absolutely loving - Halo 4, Forza Motorsport 3 - also loving - and Portal 2.

Age doesn't really matter to me, I'm just looking for some great games that veteran 360 owners have enjoyed throughout the years! Help me out?