It feels silly to do a review of Halo 3. Given the ridiculous sales, chances are you either already own it or have decided you're not interested. But it feels equally silly to not comment on the "largest entertainment launch of all time."
Fundamentally, Halo 3 is more of the same. But that's not a bad thing. You've got to remember that the first Halo established the viability of the shooter genre on consoles. We have it to thank for a successful gamepad control scheme, melee attacks, an evolution beyond health kits, more strategic gameplay due to a limited weapon load out, offhand grenades, engaging vehicles, a cooperative campaign, and revolutionary enemy AI. This game alone was enough to get me back into console gaming for the first time since the SNES. The all-nighter where I first completed the campaign (co-op, of course) stands as one of my most memorable gaming moments ever.
The first Halo had excellent multiplayer (albeit with a crazy overpowered pistol), but it was limited to LAN parties. The second Halo set the bar for online multiplayer matchmaking so high that it's yet to be rivaled. Seriously, playing any other game online is downright painful. They place the burden on you to find a server with good connection that's not empty, not full, and has competitively skilled players. With Halo all you have to do is say "I want to play," and the rest is taken care of.
The third entry doesn't deliver any more grand revelations to the shooter genre, but it does clean up its remaining blemishes. The moment-to-moment tactical gameplay has always been so intense that we almost ignored the atrociously repetitive level design. Halo 3 rights this wrong at last with some truly varied environments, creating a singleplayer campaign that is well paced, rewarding, and thoroughly replay-able. I've milked it for every achievement point available and I still sometimes itch for another go through. The multiplayer is less dramatically improved, but with tighter balance, better voice options, and the ability to review films of your matches, I'm certainly not complaining. No, the jump to Halo 3 is not as large as those before it, but there's no denying that this game is a solid package.
There are some that have called Halo overrated. I'm sorry, but they're just haters. Get over yourself, overlook the Dew-fueled frat-boy underbelly, and acknowledge this series for the huge impact it has made. The Master Chief's latest battle may not bring much new to the table, but it is a solid game and well worth your time.