Bungie parts with the Halo franchise in a fitting way - by making the best Halo game yet.
When I first played Headhunter back during the Reach multiplayer beta, it felt like playing Halo again for the first time, and that feeling hasn't been lost in the full version of the game. Let me break it down for you:
Campaign
A fun, epic tale that combines the best of the previous games and throws in a little extra (space, fellow Spartans, and forklifts, to name a few). It'll be difficult for you to focus on the task at hand when the environments are easily the most visually appealing of any Halo game, and there is of course the signature soundtrack to back it up. Another nice audio touch is the lack of English translations for the aliens' speech; it truly makes the Covenant feel like a threat when you don't have grunts yelling cute little one-liners. It's also very refreshing to have the elites return as a foe, and more fearsome than ever.
Multiplayer
As I'm sure you've heard, Firefight is back and better than ever. It's great to have matchmaking (assuming your internet can handle it; this gametype tends to lag more than regular team slayer), and nothing beats flying around in a jetpack with unlimited rockets to unload on wave after wave of Covies. Arena brings an appropriately competitive aspect to the game, while modes like Headhunter and Invasion provide fun new additions. Unlike the equipment in Halo 3, you'll actually use your armor abilities (and do so frequently and effectively). Although you may find yourself sticking with one specific ability for most games (I prefer sprint), it still provides an extra dimension of strategy, which becomes evident every time you get tricked by a hologram or killed from above by an enemy with a jet pack.
The daily and weekly challenges provide a great boost to your credits, and give you a set of unique goals to shoot for each time you play. There's also enough stats to keep anyone happy for those that have linked their gamertag to their Bungie.net account, including the ability to search literally millions of screenshots, videos, maps, and gametypes uploaded by other players. These items can now be tagged right from your Xbox, allowing other gamers to easily find something they're looking for.
The only reason I'm tempted to rate this less than a 10 is due to what feels like a lack in multiplayer maps. However, as long as you don't play the same playlist all the time, there is still some variety, and Bungie is guaranteed to release map packs in the months to come. Despite the game having only a passing reference or two to the Master Chief, I'm willing to say that Reach is my favorite Halo game so far, and any fan who hasn't picked it up yet would do well to try it right away.
Hope this review was able to help you; feel free to message me with any questions or anything I may have failed to cover. See you in matchmaking!