Geek.com finishes off their review of Halo 3; it's got separate sections on campaign, forge, and multiplayer.

Halo 3's strength is in its multiplayer, they say:

If you're looking for an outstanding, unstoppable multi-player FPS, then Halo 3 is the game for you. Gears of War has a large and dedicated multi-player fan base and it looks fabulous, but the controls are not intuitive and so it's not pick-up-and-play easy like Halo is. Sure, the bumper and X buttons might throw people off for a little while, but Halo set the standard for where FPS gameplay was going, and H3 continues that legacy.

They rate it just short of a "Geek pick" because they ascribe much of the interest in the game as nostalgia for the original Halo.