The reasons I stopped playing Halo 3 are:
1). Brawl. That was inevitable.
2). The stupid gameplay physics. I will gun somebody down with the assault rifle for like eight seconds straight (that being an exaggeration, mind you) and they'll kill me in one shot with that Godforsaken shotgun.
The only weapons that aren't n00by/cheap are the AR, BR, Sniper (including laser), Spiker, Magnum, SMG, and Spartan Laser. Everything else is cheap. Shotgun, Sword, Needler, Rocket Launcher, Mauler, Dual Maulers, Dual Spikers, Fuel Rod Cannon, Plasma Pistol, Gravity Hammer, Missile Pods, Flamethrowers, Turrets, and any other weapons I may have missed.
CoD4 is more about who you kill, not what you use. Which is why I've come to enjoy it more. Everything is near standard and doesn't really matter what you have, it's how you use it. If two people on CoD4 square-off, one person with an AK-47 and the other with an M-16, they have equal opportunity on who gets the kill. Not with Halo though. It's who gets the melee and who has the better weapon...or who has the sticks. Another thing about Halo. Plasma grenades. Did you know that a plasma grenade doesn't even have to stick you to kill you? That's right. If it lands and explodes on the ground NEXT to you, it will kill you. If you're in an enclosed space, and somebody throws a spike grenade, you're toast. If you get 'naded twice with the frags, you're dead.
I hate getting into this, because it makes me angry. Being good at Halo means nothing. Anybody can be good at Halo. Anybody can grab rockets and shoot you with them, anybody can grab a missile pod, anybody can grab a GHOST/BANSHEE (which I failed to mention earlier), and so on and so forth.
If anything, CoD4 should be superior because it doesn't have as many flaws in its design as Halo does. But once again, that's just personal preference. You like Halo better and think CoD4 should succumb to Halo's massive idiosyncrasies, fine by me. Enjoy your glitch-filled cess pool of idiotic physics.
~Jack