Well if that is the case of the term, then I really don't consider Halo to have any auto-aim. With the regular projectile weapons, I have never had the reticule stick to a target and follow it, I'm the one doing the moving of the reticule to stay with the target. If the target moves too fast for my thumb moving the targeting-directional-view thumb-stick, then I won't hit it because it will run out of the reticule.
I don't see how people can complain about the three I mentioned, needler, sticky launcher, and rocket launcher.
The needler has always had homing capabilities with the needles coming out, but I have never had the needler reticule stick to the person I am firing at. Yes it turns red when I am in range for homing shots, but the reticule has never followed the person I targeted.
Even with the sticky launcher, it does have a slight lock, but once players press the charge up button, they have to follow the target manually before the reticule turns red and locks(for only a brief moment), then homing after fire. But it is the only weapon in the game that purely locks to anything.
The rocket launcher is like the sticky launcher in that players have to keep aim manually while the lock on mechanism syncs up for rockets to home, but even with that, the rocket launcher only locks on and homes in on just vehicles, it won't do it with people.
So that is why I was puzzled by what the other poster said about auto-aim in "Halo 3/Reach being completely overkill", when only three weapons only show slight if any auto-aim and really it isn't auto aim, it is just homing after the fact of shooting. Besides two of them are alien weapons and I would expect something like that from race that is somewhat more advanced.
The DMR, Assault Rifle, Shotgun, Sniper Rifle, Pistol, and other weapons human or alien that aren't the three I mentioned, have never had any auto-aim when I used them.
But now I read again what you say at the bottom of your response "Halo is a good console FPS, so it does contain a lot of auto-aiming...", it makes no sense to say Halo has a lot of auto-aiming when only the three weapons, the needler, sticky launcher, and rocket launcher, have barely what could be seen as auto-aim. The other weapons in the game have absolutely no auto-aim.
So, taking in how many weapons there are in the game, Halo has hardly any auto-aim. Nothing but my own fingers and some luck has helped me get a few headshots with the sniper rifle or DMR.