I really can't decide how I feel about this. On one side, the huge voice change kind of takes away from the nostalgia, since it means that this is a completely different Mewtwo from the first movie (at least I would certainly hope so at this point, giving it that drastic of a change and claiming its the same one would be a little ridiculous!)
I also wonder how there even could be another Mewtwo. I've always thought of Mewtwo as being a one-of-a-kind Pokemon. As far as we knew, a single Mewtwo was created and grew up in the Team Rocket lab and then ended up destroying the lab later on, along with any information on Mewtwo. So, how could another Mewtwo exist? Im not saying I don't like the idea necessarily, I legitimately would like to see what kind of back story they give that.