Gonna just string together a bunch of observations, since right-off-the-top-of-my-head seems to be the best approach to this, to me, interesting topic:
(spoilered this because it's far too long - you have been warned :D)
Durant, yes, is sort of unimaginative. The connection between Durant and Heatmor though is a very nice touch - a steel ant and its fire anteater predator.
Trubbish is cute. Surprisingly so. Garbodor is unsurprisingly not cute. I don't mind it and don't understand the hate (I attribute it to "hate first, come up with an excuse later"). It's a decent concept, and pretty well executed.
Emolga is adorable and yes, is everything that it looks like it is and so perfectly so.
Petilil is probably my favorite from this gen, just because, between its design and its animation, it's easily one of the cutest pokemon ever, full stop. Even its color is as cute as green can get. Lilligant is pretty awesome too - looks like a fading southern belle, and fights like one too.
Cinccino is another of my favorites, but there's something not quite right about its fur, and I can't quite pin it down. It just seems like it should be a wee bit fluffier and more... attached? The way it moves is almost like it's pale, fluffy dreadlocks, only attached at the top, and it seems that it should fit more like actual fur, or at least like a stole. I really love Cinccino's expression though - it looks like it just stepped out of a limo and into a sea of camera flashes, and it looks perfect coming out of a Premier Ball.
Excadrill always looks to me like it's actually sort of thin and it's just wearing a baggy fur suit. I mostly like the design, but there's something off about the rumpled appearance of the fur, and the steel head/thing looks like it's too heavy and it's falling down over its eyes, and dragging the rest of the baggy fur suit along with it. Drilbur is a tremendous design though - looks exactly like what it's meant to be.
The whole Sewaddle line is great. Sewaddle looks just right - more leaf and less pokemon, as if, just as the dex says, it's been dressed up in something someone else made for it. Swadloon looks defensive, as it is. It doesn't have any reach (or even anything that looks like arms or legs) - it's just a face peeking out of a duvet. And I loved Leavanny from the first moment I saw one. It's a mantis, but it's also a swashbuckler - all it needs is a floppy hat with an ostrich feather, and it'd be d'Artagnan come to the pokemon world. If it hadn't learned Leaf Blade, I would've been deeply disappointed.
Sigilyph is freaking awesome - an absolutely brilliant bit of design. It's a full-on desert mystery and is just a near-perfect design. And it looks that much more awesome coming out of a Repeat Ball.
Scraggy is another great design that looks exactly like what it is, and with the bonus that Scraggy is actually a dragon. Even though it's not dragon type, it's in the dragon egg group, and if you look close it does resemble a dragon. In baggy clothes. With an attitude. The only problem with Scraggy, to me, is that it learns Low Kick too early, and the ones you can catch in-game have already lost it, so the only way to get it is to raise one from an egg or relearn it, and by the time you can relearn it, better attacks are available. But there are few examples of a move being more perfectly conceptually appropriate for a pokemon than low kick for Scraggy. I know that's not visual aesthetics, but it's still aesthetics.
Scrafty's okay, but Scraggy's the better design all in all.
The Gothita line is nice all the way through. Just really a shame they weren't Psychic/Dark dual types - that would've been more aesthetically pleasing, regardless of any effect that might've had on gameplay.
Eelektross is a bit disappointing. The concept is good, and Tynamo and Elektrik are both good designs (Tynamo especially so), but there's just something derpy about Eelektross. Between its expression and its animation, it just looks... stupid. Not "stupid" like "I don't like that so it's stupid" - "stupid" like "unable to form a thought." I still like it well enough, but it's just a bit odd.
Chandelure is... okay. Its movements are strange - a bit too flexible for mimicking a chandelier, but a bit too solid for a ghost. It might've been better if it shifted shape by sort of drifting, like smoke, rather than bending like rubber. I don't mind that bending effect for Litwick, since wax bending is easy enough to conceptualize, but it starts getting odd with Lampent and is sort of off-putting with Chandelure. Other than that though, they're great designs, and it's surprising how cute Litwick is.
Hydreigon looks every bit as threatening as it is. Easily one of the best dragon designs ever. It's a bit odd coming out of Deino and Zweilous though. Zweilous is okay, but a bit derpy. Deino, aside from the obvious superficial dragon appearance, looks for all the world like an agreeable puppy. I like that, but it just makes it strange when, oh-so-eventually, it makes it all the way to the sinister glory of Hydreigon.
Druddigon amuses me. It not only looks like it was designed by a child - it moves like the animation was done by a child. The whole effect is very primitive and dull-witted, which fits Druddigon pretty much perfectly. I think it's a great bit of design.
Golurk/Golett is another great design. They really look like ghost mechas made out of sand. I don't know if I could've even conceived ghost mechas made out of sand, but in retrospect, they'd look exactly like that.
Dwebble is a great concept and well executed - Crustle not so much so.
I don't mind the Vanillite line myself. I can see how those who were primed to find something to hate saw them and went, "Ah HA! Those are the things that I will hate!" but they don't bother me that much. I just think of them as an example of Douglas Adams' notion that in an infinite universe, every possible design of living thing anyone could ever conceive will exist somewhere or another, from which he posited a planet populated by ballpoint pens. I have no problem with the notion that an ice pokemon could end up closely resembling the things we call ice cream cones, and the concept is sort of amusing. The hate is sort of amusing too, so they get a bit of a sympathy nod from me.
Axew is cute. Axew is like a Newfoundland puppy - sure it's sort of big, but man it's just so frickin' cute. But then... yeah... it grows up. Fraxure is okay, but the mouth blades seem a bit of a stretch, and there's something about that green bit on its back and head that looks like it's got its shirt pulled halfway off. Haxorus settles down though, with more believable mouth blades and a nice nasty design.
The Klink line doesn't bother me aesthetically. I can at least see why the haters focused on it so much, since it is a bit too obviously just gears. I sort of like the way it's treated as a mystery in-game - as if the game universe is saying, "Yes, this is pretty obviously just gears, so how the hell did that happen?" Since it is, really, even though it looks like gears, and even though the haters hate it, a pokemon. For me though, I don't like it much for an entirely different reason - because its stats and its movepool seem like GF trolling us. It's got great defenses and great attack, and an awesome speed and attack boosting move, and then it's got Gear Grind, Wild Charge and Return, and that's it. Pretty much every other useful move it has is Special, and its Special Atk is mediocre at best and unboostable. And GF points and says, "Ha ha!"
Galvantula's pretty cool. It looks a bit too much like an electric tarantula, which yeah... is what it is... but I mean like a picture of a tarantula color-shifted to yellow and with electric bolt-y things added to it, but still... it's pretty cool. The only other thing that stands out to me about the line is Joltik's animation, which is so frenetic that it makes me jumpy just watching it.
I like the Lillipup line all the way through, except for Stoutland's enormous mustaches, just because it throws it a bit if it's a female. Yes - they're fur, and it's a dog, so they're not really mustaches, but still... Lillipup is cute and perky and Herdier is sort of playful and surprisingly tough (and anyone who's ever had a terrier can relate to that) and Stoutland is... stout. And packs a pretty mean wallop, actually.
Ducklett is just a blue duck (and why doesn't it get the hate that Lillipup gets? It's so much more obviously "just a duck" than Lillipup is "just a dog." Maybe the haters haven't played long enough to make it to Driftveil Drawbridge? They went out onto Route 1, said, "That's just a dog!" then turned the game off and have spent all their time since just complaining?) I do like one part of Ducklett though - it does this movement in its animation where it reaches forward with one wing, and to me, it looks like it's trying (ultimately unsuccessfully) to interrupt - "Umm.... say... I.... umm..." *Smack!*. Swanna is a great design, though it's sort of a shame that there's no difference between the males and the females, since it's a noticeably female-ish design. About a D-cup, I'd say.
Speaking of male and female, Jellicent is pretty good. There's a certain conception of the droll, overfed, underexercised, sort-of dull-witted and proper king and queen, and Jellicent nailed it. I just sort of wish they were at the end of a different evolutionary line or something, since Frillish is far and away one of my favorite designs from this gen - so dainty and wispy, the way it just floats there, and I was expecting it to evolve into.... something quite different, though I don't know what. I like all those designs, I'm just not sure about the one leading to the other.
Rufflet is sort of embarrassingly ruffled, but I guess that was the goal, and it does have those talons, even then. And Braviary looks every bit what it is - the baddest ass flying/normal the pokemon universe has ever seen.
Purrloin's pretty cute - cuter even than the norm for cat pokemon. Liepard's a great design, but the colors are a bit off-putting to me.
The Solosis line is another of my favorites from this gen. They fit together perfectly as a literal, visible, lesson in evolution. And if you haven't seen one come out of a Nest Ball, go do it right now - they were made for each other.
Elgyem is another great design. I just looked at it and immediately got it - "Elgyem? L... G... M....... Little... Green... Man!") It's that much more perfect that in addition to its psychic moves, it can learn Headbutt. Beheeyem though... I really like the design, but I don't get the connection. It doesn't look like a bug-eyed monster, really. It looks like a pimp in a low budget 70's blaxploitation movie. Well... if the movie was set on another planet, that is.
Reshiram and Zekrom are okay, except for those enormous things attached to their butts. It's sort of odd though that they don't really stand out as great designs. They're just sort of blah, really. Except for those enormous things attached to their butts, which are just sort of weird.
Oh, and Ferrothorn. The first time I hit a Ferroseed and took Iron Barb damage, I loved that pokemon. It's so perfectly exactly what it is, whatever that is. A ball of grass wrapped up in spiked metal, for some reason...
I expected this one to be a long one when I started out, but damn...
Sorry to the tl/dr crowd, though, of course, they didn't make it anywhere near far enough to read this bit anyway...