Matthew Bowers’s review published on Letterboxd :
An obvious and simplistic film, INSIDE OUT rejects the nuance and complexity of a RATATOUILLE or even a TOY STORY. However, Pixar still knows what buttons to push and how to push them -- indeed, if one were so inclined, one could almost say that INSIDE OUT is Pixar's most metatextual film yet, as the main characters spend the film literally pressing buttons to make their human feel. This feels more like an amusing coincidence, however, than an intention of the filmmakers.
In any event, the film is buoyed by strong vocal performances, particularly Amy Poehler as "Joy." Strangely, this is one of Pixar's most visually lackluster films in recent memory, though the bokeh-like texture of the emotions is a nice touch.
In the end, this will not rank among the greats of Pixar's canon. It does, however, feel like them getting back to basics and what they're good at (particularly after the disastrous BRAVE). Plenty of laugh-out-loud moments, and it will make you cry. Because of course it will.