I have never met the guy, so I can't tell you if he's cool or not. But the word around town is he plays the same character in every movie.
I can see where you're coming from, but "Scott Pilgrim vs. the World" was still an awesome movie. But why did it fail at the box office so miserably?
Could it have been because of Cera?
Could people be so tired of him already that they won't see any movie he's in - even good ones?
Check out this post by Rope of Silicon, where they go through his entire filmography and career to see where exactly Cera went wrong and audiences decided they were done with his hipster acting.