I think that Miku's V4 normal voice sounds... More clear and better than V3 which is cool but otherwise, not that exited for her update.
Her "power" wasn't very impressing for me, it sounds like a louder version of normal version for me. I'm, personally, not a big fan of EVEC system, I prefer her Appends.
V4 is technically "V3 with a little update": growling. Miku growls?!? For me Miku growling doesn't make much any sense. (Off topic but I think that for soft vocals growl is totally unnecessary *cough* Kaai Yuki V4)