Halo's never looked better. If you were a fan of the original, you owe it to yourself to check out Halo Anniversary.
If you've played Halo (which I'll assume at this point, pretty much everyone has), then this is nothing new to you. It plays exactly like it did 10 years ago. The AI, animations, frame-rate; nothing's changed. The only minor tweaks made are the option of skulls, the addition of terminals, and the added light cues, which make maneuvering some of the more confusing levels a little easier. There's also the option for co-op via Xbox Live, which is a welcome addition.
In terms of graphics, Anniversary sets a whole new benchmark for rereleases. The new engine looks great, and 343 did an amazing job at redesigning the levels. Everything looks comfortably familiar, yet there are so many added details in the environments. Activating classic mode allows you to switch back the the original game engine and compare the two directly. This feature reveals just how much detail went into updating the levels for the new engine.
The audio is more or less the same as it's always been. The original tracks, voice acting, and sound effects are all there, albeit in a less-compressed format. Weapons sound louder and punchier, and the music has little details you may have never noticed playing the game back in 2001.
Multiplayer is the only thing I'm not 100% happy with in Anniversary. Rather than include a unique multiplayer component using the original Halo's gameplay system, 343 has given us a selection of updated maps from the original Halo which run via Halo Reach's multiplayer suite. As a result, playing Anniversary online feels the same as Reach, armour abilities, and all. Some classic options are there, such as eliminating weapon recoil and using the original magnum (since the multiplayer has you using Reach's weapons), but it still doesn't feel the same. I'd have preferred seeing Halo's multiplayer updated with the same care and precision as the campaign. Aside from the competitive multiplayer, there's also a single firefight map included, which plays via the Reach engine as well.
If you're looking to recreate the same good 'ol multiplayer experience you had when you were a kid, you might be disappointed by what Halo Anniversary offers. However, if you want to revisit the classic campaign, then you'll be gleefully surprised by just how perfectly each level has been recreated in Halo Anniversary.