3. The new weapons are better
After the fiasco of rebalancing that took place via patches after launch of Halo 2, it’s important to get your weapons right. Bungie seems to have pretty much nailed it here, reworking old weapons for the better (hello, Mr. Needler) and seamlessly introducing new, bigger, boomier ones (good day, Spartan Laser, Missile Pod, and Turret).
Most of the time you’ll find you’ve got more fire power than you’ll know what to do with. You'll be switching weapons, not because you have to (since every weapon can handle just about any scenario), but rather to, you know... blow things up and watch the results.
And that’s without mentioning the new Spike grenade, which if you think looks nasty lying on the ground, imagine it stuck in someone’s visor.