The game almost feels somewhat stripped down. No duel wielding, crazy new vehicles or enemies. The objects from Halo 3, that I never felt really worked well, have been replaced with armour abilities. Some are tweaks of the familiar (active camo, bubble shields), and some are completely new (jet pack and armour lock). You also now pick your armour ability and starting weapons in the multiplayer loadout, giving a feel of different classes - a welcome addition. Overall, the system seems more balanced and useful.
You can see Bungie's affection for the franchise in the care that was put into the single player campaign. Though there is no character as memorable as some of the best characters of old, you do feel yourself being drawn into the story that never feels overburdened in the 15 to 20 hour campaign. Visually, the game looks even crisper and better, runs well, and still feels very much like a Halo game. I still found the multiplayer rather dull, but the addition of new game types like invasion, a much more robust forge mode, and a greatly improved firefight mode (much more fun than horde mode from GoW) really help the game along. Even the Halo gaming community seems more mature - likely a result of the uber-twerps migrating to Call of Duty.
Fans of the franchise can't go wrong here and even those, like myself, that have found the Halo gloss wearing some time ago may be surprised.
Immersion: 3
Interface: 5
Game Play: 4
Challenge: 4
Fun: 4