ocarina of time is up there, when it comes to single player games for its time. it was straight up revolutionary.
goldeneye too. shit was madness.
world of warcraft when it first came out (vanilla and BC) were insanely fun, but sadly those kind of ridiculously time consuming games are just bad for your..... life. but it was and probably still is one of the top mmo's of all time.
the whole battlefield franchise was amazing. 1942 was a ton of fun when it first came out, and all the versions that followed. battlefield 2 was probably my favorite of them, and probably my personal favorite computer game ever. not too time consuming, a lot of fun, great to play with friends without being too stupid and competitive. just an overall good time.
a few of the final fantasy games were loads of fun (7, 8, 10)
fucking guitar hero too. that shit was the centerpiece at many drunken parties. so fucking fun.
ehhhh that's all i got for now..