I like the idea of giving more visual feedback that you're making progress, if not actually lowering enemy hp. Some other things need to be tweaked as well. I was more or less fine with Knights teleporting to safety, but what made them suck, was the ultra-quick shield regen after a teleport. In Halo 1 an Elite remained vulnerable for a much longer time after it's shield were down and it ran away. That longer time rewarded seeking out hiding enemies. In Halo 4 you were much better served by just writing off a teleported Knight and moving on to kill or defend yourself vs the remaining enemies on the field.

Totally agree about easier headshot hitboxes. I don't want the game to be on cruise control easy mode, but there are plenty of times where I felt I got off a properly aimed headshot but it either didn't register for one reason or another. To this day I'm still not exactly sure if Knights require a second headshot like Halo 2 Brutes, or if I was missing just slightly. Something that important should be clear!

Also double yes for more ammo in the guns. Again, easy mode is not the goal, but having to track down a weapons crate after every Knight was very very annoying. In Halo 1 the base Elites were more or less balanced that one full clip of a properly used Assault Rifle would kill them, and you got 10 clips. In Halo 4 you might be able to kill two or three Elites or Knights… and then you're out… and there's two more Knights, and some watchers, and Crawlers (or Jackals and Grunts) still shooting at you. I think a good rule is that any one standard gun should, if used properly, clear an encounter. Tons of caveats and exception there of course.

I'd keep the Watcher's Hardlight Shield projection ability, and grenade catch ability intact. To me those were things going in the right direction. I liked the idea of a dynamic changing encounter that forces the player to switch tactics. The Watcher helping the other units delivered that, and it's not the poor Watcher's fault the other units didn't come through on their parts.