Is not that Chris is bad, on the contrary, he did a great job in the Lego Movie.

But unlike Charlie Day, he doesn't sound like he is trying to imitate Mario. Charlie works because of high pulls his voice as Luigi, but Chris? "Don't worry guys, Mario will be talking normal."

Come on, man. Just pitch your voice a bit.

also day's manic shrieks and rambling lends itself very well to luigi's personality, being the more cowardly and nervous brother.
It might just be me but I think the problem with the clips we heard of PrattMario is kinda flat and monotone? like if he sounded more enthusiastic and upbeat it probably wouldn't be so bad. Although as time goes on and by the time we're hearing his voice during the movie it might not be as distracting as it is in these short 1-2 minute trailers. only time can tell though