Note: Not done with the game, but I've flown, drive, and shot every damn thing possible. I'll cover what Garth didn't.
SPOILER WARNING: Uses of weapons and stuff. No story or the amazing finality of your riDe in Mission Six.
UNSC
I'll fill in what Garth missed.
SAW is just fun. So many rounds. It's only a slightly more inaccurate AR. Ammo is scarce, but man is it so fun to wade into a bunch of crawlers and blast away with that massive amount of ammo. I took down a dozen Grunts, Elites, and using the Suppressor in tandem allowed me to kill Promeathen Knights on Heroic with little trouble.
Sticky Detonator. Oh my god, it's amazing. Fire, stick, press again to detonate. Stick one to a grunt...wait till he's near an Elite, and BANG.
It's a Rocket Propelled Human Remote Detonate plasma grenade!
Shotgun. Such an epic makeover. Nothing different besides the looks.
Rocket Launcher works the same. Same with the Spartan Laser.
Sniper has less recoil.
Railgun. You get five shots. Means five easy breezy, beautiful Promeathen Knights DYING IN ONE HIT ON HEROIC. It is my favorite gun. Aim, charge, release trigger, watch your target DIE!!!!!!
DMR. Less ammo. Less firing rate. Still kicks Covenant ass into next week.
COVENANT
Storm rifle loses charge too fast.
Plasma Pistol drains fast in overcharge.
Needler Ammo scarce.
Conc rifle is alright, but rare.
Beam Rifle is rare but good.
Forerunner
Boltshot and LightRifle are the best. Boltshot because the secondary shotgun feature. LR hecause it's a BR of epic.
The Suppressor in tandem with the SAW rapes Prom Knights on Heroic very well, actually.
Incinerator Cannon. Rare, low ammo. Burns things to cinders, so a bonus.
Binary Rifle: Two shots a mag. One hit kills Knight Bandwagons with a faceshot if I remember correctly.
Pule Grenade's are tricky to use but effective.
Armor
I disagree with Garth. Promeathen Vision is insanely useful. It allows you to pinpoint enemy and allied troops in a flash. It's great for seeing THROUGH corners and such, pinpointing enemies and slaughtering them.
Camo's okish.
Hardlight was useless to me.
Hologram was semi useful for diverting fire
Never used autosentry.
Jetpack is Jetpack. Can't go wrong!
Thruster Pack: think Jetpack, that gets you behind enemies. Now have it when fighting Hunters. Enjoy!
Vehicles:
Warthog sound is too high pitched
I avoided a Mongoose.
Scorpion is as epic as ever.
Mantis Mech: Put a Falcon chaingun on full auto on one arm, put a Rocket Hog launcher on the other, make it twice as tall as a scorpion with shields and the ability to rape Phantoms in three salvos. On Heroic.
Mamoth: Target Detonator, and the miniMac purges
Two more UNSC vehicles. But why spoil th amazing surprise?
Ghost: Same as before.
Wraith: I blew them up.
Banshee: on Heroic? Paper airplane in a flamethrower.
Gameplay: Pure. EPIC.
Honestly, Halo 4 lived up to it all. It has lived up to it. If onoy the Warthog would get a noise change back to normal....
Anyways.
Mission 6. Enjoy Commander Lasky's present.