He's gotten fat. I'm not fond of this new "shell" of his, specially after it's left him with a gigantic obvious weak point. The previous weak point was at least INSIDE of him.
And it seems that those spikes around him are either weak points or they are fired out to attack you or something. I honestly thought his two beam/shot attacks were enough, but perhaps this will provide with some variety. The bigger mouth/tongue makes him look like a gigantic frog head on top of a snake body. His shell's "legs" or tentacles or whatever don't seem to provide any function either, and seeing as I only see one tentacle far away, it makes him look like a t-rex with tiiiiiny hands.
That light-ish horn of his seems to be the weak point this time around, rather than going inside him at enough speed and bursting out of his mouth, making him explode. Overall, he looks less scary, more goofy and weaker. I don't really like this new design, but all of this is honestly my opinion in terms of asthetics. It kinda seems like they're tacking on useless crap on him. Reminds me of the changes that classic japanese Godzilla got in the american 98 Godzilla movie. It's like piling useless crap on a perfectly fine design which doesn't need any changes.
Also, Don't forget that Sega does not know what they are doing, remixing Egg Dragoon to ACTUALLY look menacing, making that Egg Bot look cool and making Silver competent? What is this? not to mention that Perfect Chaos' graphically inferior, dog-like, and over-mechanical original is changed into something that is an actual CHAOS being?! Sega, YOU SU-
Okay, I can't keep this up any longer, are you a sonic fan or my friggin' English teacher?! Sega upscaled Chaos' look and redefined him as, not a water monster solely, but a being of chaos! He looked kinda hilarious during the Dreamcast era, seeing that he looked like he was "sniffing" the air; Chaos was meant to look like something not belonging to this universe and a spirit of the Master Emerald, hence the green glow, the weak point was made for gameplay purposes, not for storyline logic.
New Perfect Chaos looks perfectly fine, pun not intended.