Brilliant! So, in addition to Portal 2, download a game called Braid from the xbox online game store, if you can. Again a puzzler but a platform one involving time manipulation. Each set of puzzles is set in a context of how we perceive and relate to time. It is profound, beautiful and deeply philosophical and the closest a game can get to art, in my opinion.
Braid and Portal 2 represent two of my most memorable and valued gaming experiences.
Sorry, going off on one now, but Ghostbusters is also really, really fun! ... I'll leave it there. Promise.
If you end up playing either of those games do let me know what you think!