Details from the February issue of Game Informer are as follows.

• Halo Reach is a prequel, but the characters are not those featured in Eric Nylund’s book Halo: The Fall of Reach. The entire crew of Spartans, codenamed ‘Noble Team’, have never been seen before.
• There will be new weapons such as the Covenant Needle Rifle and the Human DMR sniper rifle, but some old weapons will be getting an aesthetic downgrade due to being older tech. However, each weapon’s unique sound is more pronounced due to better audio tech.
• The air-craft from the trailer released at the Spike VGAs was a Falcon, a new small drop ship for ferrying Spartans behind enemy lines. Civilian vehicles can also be driven in combat when found in the battlefield.
• Stealth will play a bigger role in Halo Reach, with the ability to assassinate enemy troops instead of simply shooting them.
• All the multiplayer features from Halo 3 will return, in addition to some new armor customization that may affect gameplay.

Other cool stuff: