Ace combat is ok, but cod4 still sucks imo. I literally hate that damn game and ea's release the same game every 3 months stragegy. If you go off of sales obviously halo 3 comes to the top. Assassin creed was pretty good if you enjoy long slow games with action sprawled about occasionally. mass effect is getting A lot of heat and should be worth a try.
Best graphics is still Gears of War though. You have got to at least rent dead rising... hilarious game that zero punctuation never did a review on
You should probably try Game of the year: Bioshock.