I myself have to admit the starter's final evos of Gen 6 look fairly great. I mean, its without a doubt that the whole Knight/Mage/Rogue theme has been reached. Overall, however, the main problem with some being disappointed of the designs, is that some people once again expected WAY TOO MUCH from these evos, and if it doesn't match their expectations, it suddenly sucks or what not. This is without a doubt a repeat of Gen 5's starter evolutions where people claimed they were 'fake' and went to numerous methods to prove that. It also doesn't really help the games were released 11 days eariler and people spoiled a great deal about Gen 6, atleast to me. Then again, when potential real leaks appear...I agree...its way too hard to ignore them, even for me.
What I'm trying to tell here, however, is that for the future next gen (in general sense mind you) whenever starters are released for the first time to the public, people should try to lower their expectations for their final evolutions, although I'm sure this will be fairly hard to do. Try to lower your expectations, and the overall result might be less disappointing and more acceptable, even if people make possible guesses with fanart and such, just in case a starter evo ends up looking bad to one's eyes. Because I didn't think about much how the evos would be appearing in Gen 6 or obsessed myself with them to the point of obsession, I'm fairly alright with their designs. People, due to the leaks, are either pleased or displeased, but I ask that for those who are displeased, that you wait for the official Sugimori style art first. Perhaps then, things might be better....(or not).
Going for opinion, while most seem to dislike Delphox, of all three starters, its the only one to keep its ear-motif through out the entire line. Also for those who complain the evolution has no wand/stick/twig/whatever, I tend to think that the twig in the middle stage was more like a assistance for the second stage evo of Fennekin to help focus its psychic abilities as it grew. Furthermore, Fennekin's first form has no twigs whatsoever, other than the entry it likes to chew on them, so the twig was never really a part of the design to start with, thus a complaint that really makes no sense.
If anyone thinks the same way I do when it comes to Fennekin that way, its final evo practically has no flaws, for the twig wasn't the motif, it were the furry ear tufts, which just grew bigger with each transformation. The robe and sleeves are also addtional fur to the design, helping a lot with the mage theme it has ongoing. I'm really thinking to go with this starter just because of its completeness.
For Chesnaught, I really love its design and typing. The only negative part about him is his color scheme, in which his primary colors were switched with its secondary colors. It if maintained its original color scheme from its first two forms, it would have been a lot better, but just because it has a different color scheme, doesn't mean he's bad in any way. I am just optimistic here and look at the starters with a fair gaze, instead of dramatically complaining who doesn't get what he or she wants. Maybe GF has a reason why they did this, but perhaps the official Sugimori art will be better as I stated before.
For Greninja, when it was first leaked, I honestly didn't know what to say of it, but I do agree with many people that the tongue scarf is unique without a doubt, and also invokes that ninja feel quite well along with its unique move "Water Shuriken". Prior to complaints about him, this evolution too, keeps some of the features present; mainly it builds upon the darker shade of blue, its bubbles become its mask (I think) and turn streamlined, and its eyes build upon the spikey motif they have. The eyes are also still yellow and completes the ninja motif.
Overall... People just need to try and lower their expectations for future generation starter final evos, even when the hype or any possible fanart is super great. That way, any disappointment will be greatly minimized and not be so overblown in large obese proportions, and acceptance will be around much quicker.
Don't judge a book by its cover.