While a better choice by far than GOTG or most other IP's, this still evicts a classic ride (of the sort you don't see built anymore and probably never will again) and offers no gain of additional rides. And as Martin hinted, it's unlikely to be even half as long as GMR (we'll be lucky if it's a third).
I'll somewhat hold my judgement until we see the final product, but i've other concerns as well. In the proper hands, with the proper budget and with the right execution, this obviously has the potential to be an awesome ride. But I have serious concerns about budget and execution. Budget was already mentioned to have been somewhat reduced in an earlier post, so that's off to an unpleasant start already.
I also feel somewhat troubled by
@marni1971 hinting at a heavy presence of video screens. While a great ride, Mystic Manor IMO is already a bit too screen-centric for my tastes. And while I may be attacked for saying this, even the POTC at Shanghai (in spite of being a good ride with well implemented screens) went overboard on screens with too few animatronics for my tastes. Ratatouille looks like it completely crossed my threshold of tolerance, wouldn't like something like that at all.
I miss the detailed setpieces and huge AA population from rides like Splash Mountain, following that ride's type of showscenes are what I would have wanted out of a Mickey Mouse ride. I'm even more concerned that they'll use CGI instead of traditional animation for the video (something they tried to do with Little Mermaid initially, and even recently for a Snow White's scene at Shanghai), which would be extremely inappropriate for classics.