GameSpy wants you to know they love Halo 3. They really do. It's just that 2007 was just too good a year for the console, and well... a game that executes really well on a known formula while tinkering with details and adding some new features just isn't quite enough to make the top half of a top ten list this year.
Halo 3 is a carefully tuned refinement of one of the most successful game formulas of all time, and innovative gameplay mechanics don't really figure into that equation. So, while Halo 3 accomplished amazing things in terms of its impact on the burgeoning Xbox Live community by introducing the Forge (object-oriented level editor) and an impressive set of video-editing tools, the frenetic multiplayer remained mostly the same, with just a few tweaks (HD graphics, deployable equipment, new guns) to bring the experience into the new generation.
Ironically, the Halo game even Halo lovers love to hate-- Halo 2-- got comparatively more accolades than either the original or the final chapter, despite the fact that many fans like both of them better.
Oh well. So Halo 3 takes the #6 spot, behind Mass Effect ("brilliantly stylish"), Rock Band ("magical balance between musical experience and videogame"), Orange Box ("best gaming deal of 2007"), BioShock ("a beautifully designed and wonderfully thought-out world") and Call of Duty 4 ("It isn't set during WWII!").