I'll give my thoughts on all Gen 6 mons that are fully evolved:
Chesnaught: I don't think it's as bad as people say it is. Though I expected this to be the fast badass one, and Froakie's final evo being the bulky-looking one.
Delphox: I love Fennekin, and I'm glad it's not Fire/Fighting, but it leaves a lot to be desired.
Greninja: At first, I was mixed, but I love it now.
Diggersby: I don't think it's ugly, and it's pretty useful in competitive IMO.
Slurpuff/Aromatisse: I think they are ehhhhhhh (Can't decide IMO), and they are just NU hype trains, but Aromatisse I heard is good in Doubles.
Florges: I'm not a huge fan, and I prefer Floette (I think that thing's adorable)
Sylveon: I freaking love this thing. It's useful, and I think it's cute (Even if it has Bug eyes)
Vivillon: Very cute for a Bug-type, but it's not too scary for a 666 Pokemon.
Pyroar: Cool, but it could've been better in stats.
Pangoro: Same as Pyroar, but I love it's design a lot more.
Gourgeist: My favorite of this gen, even if it does kinda look like a dick.
Dedenne: I don't like this thing, but it's cute, but even then, it's weak as all fuck.
Furfrou: I wanted it to have a Toy Poodle Pre-Evo, but oh well, it's alright I guess.
Carbink: What is it supposed to be?! A bunny, a flying gem? What is it?!
Trevenant: I like this one a bunch, and it's very close with Gourgeist, Ylvetal and Greninja for my favorite of this gen.
Klefki: It's unoriginal, but it's annoying as shit in competitive (It's good, don't get me wrong).
Aegislash: It's a hypetrain IMO, it's so predictable in competitive, but it's so awesome.
Barbacle: I like this one, but it's very weird.
Dragalgae: Kinda reminds me of Kingdra, but a bit more icky.
Clawitzer: I love this thing, but I never got it's huge claw, maybe it's origin has that, but I'm not sure.
Goodra: Icky and cute at the same time. But I love Goomy a whole lot more.
Talonflame: Basically what I said about Aegislash, and it's actually not Normal/Flying for once!
Noivern: Pretty nice, but it looks a bit too much like Swoobat IMO.
Aurorus: Good design, typing and stats, not so much.
Tyrantrum: An actual T-Rex, and it's pretty cool.
Heloisk: Suprising gem in this generation, pretty nice.
Gogoat: It's interesting I guess.
Avalugg: It's part reptile, part roadkill, part ice berg, yeah..........
Hawlucha: Same as Helioisk
Meowstic: It's cute, but it's debatable in competitive.
Malamar: Pretty wicked IMO.
Zygarde: It's a snake and worm mixed together, but it's design is pretty weird.
Ylvetal: Favorite of the two legendaries, but I had to go with X.......................
Xerneas: It's a Fairy-type deer, which looks Steel or Grassish, and it's pretty good in it's own right, but I prefer Ylvetal.
If I missed any, sorry for that.