People need to except the fact the the old Sugomori artstyle is gone. and stop hating on the newer monsters.
People don't like change.
Gen V set standards Gen VI didn't even begin to live up to.
I will agree that I like more designs in Gen V than in VI.
But that's because there are a host of more Pokemon to choose from. The percentage of designs I like in Gen VI are probably much higher than any other gen. There are very few (seriously, like 5?) designs that I don't like from VI. Even some of my least favorite types (Normal, Fire) are looking good this gen.
But... gen 4 was good. Not that good but good nonetheless.
In my opinion Gen 4, 5 and 6 designs are lot more creative than, let's just say, Gen 1 and 2 dsigns, especially Gen 1, my god Gen 1 had some of the most bland and laziest designs in the entire franchise.
Gen 1 showed a LOT of its development in pretty much every aspect of it, including designs: A ton of the pokémon are dinosaurs. Almost all are "animal with X".
This makes sense because they were just trying to make a generic monster-collecting RPG at first, but I don't get why people praise them as "better" when they do have much less work put into them.
And I don't mean subjectively or what I think, I say so because that is what I conclude based on all the interviews and different analisys of the games.
Like, I'm not talking about the quality. Later pokémon do have much more specifically researched and carefully stylized designs: You hardly find an animal near as-is nor something based on simply a general thing in later generations. (Although sometimes it does show up)
Whether THAT is a good thing or not and if you like it is something else.
This is even observable between Gen I and Gen II: Just contrast the cartoony Miltank with the realistic Tauros. Or the two fighting-stlye 'mons with the more out of left field specifically capoeira Hitmontop.
Or look at how the legendary Beasts have a more complex design than the Birds and Arcanine together.
Ultimately though, as a mater of taste, this more work does lead to more specific designs that some people may dislike. Which fair enough, some may find simpler things more appealing. I'm perfectly okay with that.
But they're not objectively worse when the only objective thing is that they probably took longer to make. (Again, with exceptions)