Personally disliked the fact they changed the character designs.
The orignal looks for the characters were fine the way the they were, but as far as the characters that had signifingant changes, they looked horrendous in my opinion.
As far as gameplay, Crash of the Titans and Mind over Mutant focused too much on being mostly beat-em up that has you depend on mutants to make it through parts with the okay platforming as opposed to having great, fun levels that were challenging to beat and had something to make them unique.
Collecting gems, relics, and crystals gave you a sense of accoomplishment, whether you just simply beat the level, break all the boxes, or sped through the levels. The bosses put up some sort of fight all the time, the bosses in Crash of the Titans and Mind over Mutants are complete jokes.
If they make a Crash game that goes back to the roots of the series, they still need to be able to add what made Crash games fun and what will make the new game fun.