My biggest problem with new pokemon, outside of re-used concepts like you mentioned, is the way they are made.
Most gen 1 and 2 pokemon have a solid design going for them, simple and memorable, based on an existing animal (or a combination of one with something, like mashinery), has a leading colour thats subdued enough to not look ridiculous, basicaly, they looks like they could exist in an actual eco-system.
Agreed with you, for the most part - especially on the eco-system. I guess that may explain my preference for generation 3, I always felt that the choices in the dex portrayed their respective locations really well. I know generation 3 had a fair amount of random animals with a type slapped onto them, but I felt it worked.
There's always exceptions to the rule - both in early generation designs and "later" generation designs (generation 6 is completely different from the "later" generations, most of the designs in this generation are pretty awesome in my book).
Druddigon here is just a mess of random shapes and bright colours. So many new pokemon are now just a bunch of squares and triangles and circles with ultra-shiny reds and blues and yellows in a vague shape of an animal, like its a Picasso painting without intending to be one (and even THEN that idea was already used much better on Porygon). Either that or its a re-used idea, like another bird pokemon, or another moth. There are some good ones, sure, but so many of them just look so friggin ugly, ugh.
Personally, I feel like Druddigon is one of those exceptions mentioned above. See, everything about Druddigon screams
"don't touch me or you'll be in a world of pain" to me - from its abilities Rough Skin and Sheer Force to his palette. The amount of spikes on him speak for themselves and fit in pretty well with that particular idea. His bright colors (both its normal palette as its shiny one) remind me of real-life poisonous frogs - who use their bright colors to scare off predators, signaling them that they are not to be messed with.
I can understand if people don't like particular Pokémon but I don't know, I feel like Druddigon is one of the few Pokémon in generation 5 with an actual idea behind it.