Sonic appealing to Nintendo/Mario fans = the death of Sonic. Sonic needs to be his own thing, get his own audience and become popular off of that. Not become a 2nd rate low quality Mario platformer. Which is exactly what lost World is being seen as by Nintendo fans, a Mario game that isn't as good as Mario.
Don't get me wrong, I'm not saying Sonic has to be boost to win to be good, but come on, trying to be a Mario game is a really bad direction for Sonic.
That's my opinion.
I'm on both sides of the coin.
Sonic's references to his past badniks and the more Mario like level approach is definitely something that has improved for me regarding the Sonic games.
But yes...Sonic plays like a fast Mario, but the controls are even worse. The one thing Sonic should be copying Mario from is the controls. It doesn't need to be 1:1 with Mario, but to a point that Sonic's homing attacks work whether you are "locked on" or not would have been good...since I died on Zorak many times because of the really stupid way it locks on...look away and the lock on is lost...especially the five tiered Homing Attack build up, which sucks....
The power ups (Wisps in particular) are executed horribly in this game...whereas in Colours they worked...so I don't get what Sonic Team are trying to do.
Some of the Mario copying ideas are good (collectable Red Rings, level design is actually better since I can see the pretty world and even the level structure are what I believe are the good points from Mario), but some of the ideas are not so great (Wisp Powers, which use gimmicks and are worse ideas from Mario's more 3D World like power-up system, the controls & parkour system (I still don't get how you run across walls from the vertical run) and the boss fights).
What I think they messed up on entirely is the difficulty spikes you encounter in the game...unless you really remember every single thing in the levels, you will die...a lot. Mario's not necessarily difficult per se (the new ones like 3D Land and NSMB), but I always find the challenges fair. Sonic's gone the opposite direction and made it harder to do due to the bad controls.