Metacritic is a pretty good site to track the scores of various reviews of the same game. So far, after about a dozen reviews HALO 2 (PC) is averaging a 72 out of 100. The scores range from 92 to 60. That's a pretty wide gap.

Track the reviews at Metacritic.

By the way, my local Circuit City had one copy of HALO 2 (PC) on the shelf.