Ratchet and Clank: Tools of Destruction is my personal favorite from that year.
Out of the poll options, I went with Portal, but even then Bioshock and Uncharted are up there with my favorites. Also, even if I haven't played it for years, I can't discredit how many hours I spent playing Rock Band 2 at various friends houses for at least 2 or 3 years after the game came out.