Subjectivité, quand tu nous tiens...
My own Likes/Dislikes (other entries are assumed "Don't Care") on MM art, for your ignoring pleasure:
Like:
Bulette. That landshark definitely has style (and the axiomatic one in the MotP is even better).
Demons (Glabrezu & Vrock).
Devils (Osyluh & Cornugon/Pit Fiend). Well done, but I'd like to know if the red thing is a cornugon or a pit fiend (both descriptions apply to the pic). Definitely needs more of these outsider drawn out (all, as I think they'll do).
Dragons. They are cool, all of them, only reproach I have is the Silver's head.
Dragon Turtle. Good.
Dragonne. The pic compelled me to use the creature.
Giants. I'd have liked to have the other giants, though.
Giant Eagle. The beast is well drawn. The elf on its side, though, is a miss, and don't seems to belong to the picture.
Giant Owl.
Grick. Although the colors don't match the illo.
Harpy. Although I liked the "natural harpy" concept sketch, that "monster from hell" is really well-done.
Hippogriff. The beast seems plausible with that artwork. Illos I had seen of this chimera before looked rather like "cut'n'paste" of animal parts.
Hobgoblin.
Kobold. Ain't it cute ? It pushed me to write a little kobold adventure, as I wanted to game with kobolds.
Mind-Flayer. It is supposed to have big, bulbous eyes, but the little eyes just make him looks nastier.
Minotaur.
Nightmare. Impressive creature with an infernal nobility. Great.
Nightshade. One of the most frightening monster thanks to that damn illo.
Pegasus. Beautiful beast.
Planetouched. Like'em both.
Remorhaz.
Sahuagin.
Sphinx. Another creature I wanted to use because of the illo.
Troglodyte. Great illo.
Yeth Hound.
Yuan-Ti. I only wish a half-blood would have been put in the group.
Dislike:
Allip. It should at least look somewhat like the description.
Aranea.
Beholder. I know they vary wildly, but this one looks like a Mouth Tyrant more than like an Eye Tyrant.
Belker. Bad, badly done illo.
Couatl. For something legendary for its sheer beauty, it is really disappointing. Something like the Lillend (without humanoid part, of course) would fit better.
Devourer. Don't like the style of art.
Digester. Admittedly, the monster is ridiculous to begin with, but a good pic could have turned it into something usable.
Displacer Beast. That one seems to have prayed only on some few ukrainian mice these days.
Drider. Dark elves aren't green, driders don't spin webs, and I don't like the way it is drawn.
Ethereal Filcher. But that's not really the fault of the artist (although he did get the colors wrong), since the monster is silly to begin with. It's still better-looking, in a way, than its cousin the Temporal Filcher in the Psionics Handbook.
Ethereal Marauder. Same comment as above. Don't like the creature, find the pic stupid, even if I rather like Despain's work.
Ettercap. It looks like nothing at all.
Gargoyle. I don't see how the creature can bite, as it lacks half its mouth.
Ghoul. Purple ? Colors are bad. Plus, the art is bad also.
Gibbering Mouther. These things are hard to draw, I acknowledge, but still it's a miss.
Gray Render. ???
Griffon. Don't like the art, and neither the pose of the beast. It looks like a pigeon.
Grimlock. Again, don't like that style of art. Plus, they are supposed to lak visible eyes, but the shape of the eye is there.
Hag. First, I'd have liked to see all hags, then that one is just a miss. A spindly, skinny photosynthetising old woman. Not even really awful-looking: compare with the night hag.
Hell Hound.
Homunculus. Urk. And the head, the head ! It don't looks like anything. (Oh, and pet peeve of mine, I know they're supposed to be ugly and warty, but since their shape is chosen by their creators, I would imagine a look a bit more "Tinkerbell" and a bit less "Flying polyp".)
Howler. Quills are too long, there's no way it can pierce a biten victim with its neck quills -- and there's no way it could be rided.
Kuo-Toa. It looks more like a frog than like a fish. The DiTerlizzi illo was much better done.
Manticora. No, it's not the head who bug me -- the creature is no longer supposed to have a big human head. It's just the style of the art I don't like. And the "beard spikes" are overkill.
Medusa. Scales are too large, I don't see how the creature could be undistinguishable from human at 31 feet or more. Except if she wears a burqa. And her foot ! Is that toes or carrots she have on her foot ?
Mohrg. An illo that is a picture of the described monster would be better than something that only shows the artist hadn't read the description.
Mummy. WAR is popular on these boards, but there's a problem with his illos, they are all the same. Monsters with triangular feet bigger than their heads, fists frequently even bigger, a shambling, hunchbacked pose, and big, misshapen mouth.
Nymph. A beautiful, well-painted, POSING HUMAN WOMAN.
Phasm. Bleeeeeerch. Even ignoring the fact the illo is one of the ugliest in the book, I question the wisdom of comissioning an illo for a creature who take the shape it wants (and thus, will never be encountered under that guise). It's a blatant injustice that the phasm got an illo, and not, for example, the pseudodragon.
Rast. The monster is idiotic, but the illo is even more.
Roper.
Spider Eater. It's ugly, its wings look like old umbrellas, and its tail is just wrong.
Sprite. Proportions are all lost in space (do you have the feeling is pixie is in the same size category as an halfling ?), and the art is just awful.
Stirge. Not too badly done, but don't really match the description. Furry body meant, IMO, like a bee. And 4 isn't eight. And there aren't any pincer. And...
Tarrasque. The concept art was so much better. If at least the artist didn't confused the eyes with the ears, and the nostrils with the eyes...
Titan.
Umber Hulk. the illo is mostly good, but those poor rear legs...
Unicorn. Bluuuuurch.
Wraith.
Wyvern. (But my bigger concern with the wyvern is its punissimus Strength score, not its art.)
Xorn. I've seen well-done worn illos, and they didn't looked like this mutant toad.
Vampire.