If you posted spinnies of these heads i'm sure I could point out one or two more minor things.
Hungover Beethoven:
The raw skill within this is incredible, I could actually show this to someone and they would know(Well, a smart-ish person) and they would know who it is. Although, one of the things I would like to point out the noise looks rather fat and 'box-ish'(No box, i'm not talking about you, I mean a real box). Like uhh, it should curve more and be more natural shaped, like this(I didn't makes this, it's a image from google).
See how it curved in and then back out? Think of it as some sort of mutated hour-glass(Even though i'm pretty sure you could nail the mapping if you gave it a small edit, i've seen more of your work a long time ago, my join date lies).
The other thing I would like to point out is the white strands of hair upon this great mans head. They look to thick compared to the rest of the hair strands. Especially the ones on the middle part(His 'fringe'?)/above his face.
7/10.
Monobi:
Me likey, the one thing that put me off is the reflection in his eye has its own outline rather than going over the top of the iris/pupils outline. You created a head for me a long time ago which was basically just leaves with two glowing eyes coming from within. If you still know where that as I think that the leaves you drew on that were very nicer than the current ones on this head and would fit in faaar better.
I do not like the back of this head, I have no idea what it's supposed to be but i'm assuming some sort of plant/bush/berries/thorns? something along the lines of that anyway.
The one thing I have to point out is how well you have made the 'upper lip' part, seriously. I almost jizzed in my pants when I noticed it, it really is the highlight of the entire head.
Olguh:
I hate this head very much. Don't get me wrong, there isn't a major reason I don't like it, it's just not my type of head. I don't have any negative CnC for this head, however. In my own opinion you could create a second version I think would look much better.
1. Circulaur eyes.
2. More depth less blur on some parts of the teeth.
3. More definition on the 'eyebrows'.
4. The metal 'pipe' isn't the same size all the way around(If this was intentional dis-regard this).
5. More shading/depth underneath and around the bottom of the mouth.
6. No random lines on the 'brain'. It looks horrible.
The one thing I think is great about this head though is the skin part in between those metal pipe parts and the 'brain'. I love how you shaded and outlined those vein type things. Really superb.
Please don't take any of this as insulting or whatever, that wasn't my intention. I'm just harsh with CnC alot of the time.