Of course he could have been pulled off without CGI. In fact they originally filmed him that way. This is what they couldn't have achieved with a mask, not one that moved and was as expressive as the mo-capped actor's face:
The proportions are just too far off to put a person's face under there. The Engineer clearly has human features.
Another example then, the Predator is regarded as one of the most realistic-looking creatures ever put in theaters, in 1987, and his head is way bigger than Azog's would have needed to be. He even had great, imposing expressions as well, through his mandibles and eyebrows, etc. Remember this is
1987. What could be accomplished today?
It's funny you mention the greater depth of expressions, as one of the things I didn't like about Azog is how extreme his facial expressions were at times. Sometimes when he'd talk, his mouth would open abnormally wide and his lips would move in every direction imaginable, for no apparent reason. Makes him look even more fake and unrealistic.
If they made Azog with makeup or a mask then they'd have to change his design and bring his eyes in much closer together so that he'd look more like Yazneg or Lurtz (which is what they were not going for.)
That's your practical Azog right there, but he was so far off from what they were going for they had no trouble renaming him and showing him interacting with the "new" Azog. That's how differently they looked from one another.
I'd chalk that up to the design, not the practical effects. That looks like an average grunt orc, and an ugly one at that.
If they had to sacrifice some exaggerated facial expressions and having the eyes so far apart, for the creature to actually look REAL, then I'm all for it.
Another thing that's been mentioned, why the hell were Azog and Bolg so enormous compared to the rest of the orcs? The Uruk'hai were supposed to be these unnaturally strong and large, monstrous orc hybrids, but that's all pointless if regular orcs are even bigger than them.
I'm starting to realize that I actually kinda like Azog's design...when I'm looking at a statue or bust. It's the shoddy video-game esque look in the movies that's turning me off to it. I'm never going to like Bolg, the goblins or those pseudo-cave trolls though. Yuck.
There was some pretty bad CGI in Promentheus too at times. And some bad practical effects as well.
Really? Like what? If there is one thing that people universally agreed upon with that movie, it's that the effects were top notch.
One of the creatures in the film, the mutated Fifield, was originally CGI, but they redesigned him and used practical effects and he came out looking not only more realistic, but scarier as well. The complete opposite of what Jackson's done with the orcs.
The trilobite (baby and adult) were practical and looked fantastic. The hammerpedes were practical, like facehuggers in the previous films, and looked fantastic. The deacon was actually a puppet I believe, and it also looked very life-like. The Prometheus and Juggernaut ships, the vehicles, David as a severed android head, the space suits, the pyramid & ampules, the 3D universe map, all of the enormous set designs, etc.
I can't think of one scene that looked "pretty bad" effects-wise.