After having not played both SP's for at least over a year, I replayed U2 and U3 back to back a couple days ago; and while my opinion of U3 has improved, it is still vastly inferior to U2 because of the terrible combat and encounters.
Here's the #1 reason U2's combat is superior:
- A guy (unarmored) rushes either at me, or between cover: I shoot him, he flinches, he stumbles, he REACTS to getting hit by a projectile moving 600+fps.
- In U3: the same scenario as above, only this time, the guy scurries around like a goddam cockroach and brushes off bullets like I'm throwing marshmallows at him. Unless it's a 1-shot-kill weapon, they hardly ever react to being shot -- even getting hit with a shotgun, they will flinch but they just keep on scurrying, never missing a step.
That + the atrocious enemy spawns leads to nearly every firefight playing out the same way: kill who you see from where you are at the start of the encounter; when they're dead, turn around because you're about to be shot in the back by materializing goons; rinse and repeat until Drake returns to his jogging animation.
The movement controls are also much smoother and more responsive in U2; whereas in U3, not only are the animations stiffer and less fluid, but Drake constantly gets stuck on corners/walls which was never an issue in U2, and spazzes out into strange reaction animations when you bump into a wall or NPC.
Not to mention his obsessive need to hover his hands 8 inches away from damned near every structure he passes -- he touches more walls in 10min than I have in the last 2 years.
If the combat was as good as U2, I would still rate U3 lower; the barely-there villains; the there-because-it's-cool Shityard -- err, Shipyard -- and the retread of U2 setpieces with a twist, keep it from approaching U2 territory.