FiringSquad says that Halo 3 mostly delivers on the expectations built up by the previous two installments, providing a fitting conclusion to the trilogy:

So has Halo 3 lived up to the massive attention and hopes for fans of this franchise? Based on playing the single player campaign and checking out its community and editing features we would have to give it a qualified "yes" but again we will have a separate review for its online multiplayer features.

FiringSquad gave Halo 3 a rating of 92%.