The Battle Rifle is a new addition to your arsenal. It's an extremely versatile weapon, capable of being both a semi-automatic weapon for close range, and a sniper rifle for long range. Featuring what looks like a 2x zoom, the Battle Rifle will probably be a more advanced replacement for your pistol from Halo: Combat Evolved.
Although little information is available about other weaponry, the Master Chief seems to be able to perform some type of melee combo with the Battle Rifle. It consists of a swipe left, a swipe right, and then an uppercut.