Imagine if Mario Galaxy was never a good game, that's Lost World in a nutshell.

Sonic Lost World is a good game, but it doesn't always feel like a Sonic game and I think that's why the reception was mixed.
The Mario Galaxy comparisons are valid and the 2D physics are trash, but the 3D gameplay can be a lot of fun. Overall a fun Sonic game that I believe gets way too much hate.

It's not too fast or too slow. It's a good mix of pace.