Yep. In even an average game of Halo 4, the following things can be one hit kills: Plasma Grenade, Boltshot, Shotgun, Scattershot, Sword, Hammer, Rockets, Gauss Cannon, Scorpion Cannon, Banshee Bomb, Mantis Rocket, Splatter, Sticky Detonator, Railgun, Spartan Laser, Sniper Rifle, Beam Rifle, Binary Rifle, and the Incineration Cannon. I may have forgotten something. The needler, in any open space, is certified death too, it just takes a split-second longer than the above. And my opponent can have any of these unexpectedly at almost any time. They can spawn with two of them. And even if I kill someone bearing these ungodly gifts, he can respawn and rush back to finish me before my shield recharges.
Everything in Halo 4 is reactive: something is always happening faster than you could reasonably anticipate or plan against, and you have to respond immediately or die. No longer do I coordinate something with teammates and execute it, and if we try to do that something will happen midway through that causes that plan to spiral off in some completely unexpected direction, because of a surprise AA or an unpredictable personal ordnance threat. I can't keep people informed about who has what and where or when, because ordnance and instant respawn means that information is outdated in seconds. I can't tell them who or what is on my X, because I don't
have an X, and anyway whatever it is won't be there in 12 seconds. I don't have to tell them where I'm running the flag, or where our enemies are running the flag, because that information is available to all in a way that forces those decisions to be less interesting.
And if the game isn't objective-based, there is nowhere I have to be. I don't have to move out of cover. I don't have to leave a fortified position. There is no predictable resource that my enemies can take from me (apart from some vehicles on the bigger maps, though I don't know if they're on a predictable timer) if I simply turtle and rack up my own personal ordnance. The map's flow is solely toward those locations where I can hole up with buddies and camp -- even spawn camp -- attackers. In a game where everyone can spawn with a 3x scope weapon and has regular access to three weapons that kill in one instant shot across the map, movement is downright risky. The only reason to move is to get back to whichever familiar front it is you are either attacking or defending currently (e.g. Complex rooftops, middle base on Vortex, the 'hill' in Longbow). It's the top of Ivory Tower on Halo 2 writ large, only no rockets and sword spawn below. They spawn in the hands of the team on the top floor, because they're already winning. The fact that I'm on that team more often than not doesn't make it any more fulfilling.
Edit: Fuel Rod Cannon. The Fuel Rod Cannon is also a one-hit kill.
Edit 2: And the Wraith's shell.