I was never a huge fan of Mewtwo's original design, but I think he's one of the coolest characters in Pokemon. I prefer the original Mewtwo's design to this new form/creature, but aesthetics are only skin deep. If Game Freak can come up with a great storyline to explain this thing's existence, it's all good. I wouldn't use it on one of my teams or anything, but it has potential.
Personally, I think there's one possibility about this that could be interesting to consider - who's to say that this thing is going to be a pure Psychic-type like our old buddies Mew and Mewtwo were? Out of all Gen. VI Pokemon revealed so far, only the Starters have had their Types revealed. For all we know, NewMew could be Psychic/something else. (Psychic/Electric seems to have already been speculated.)
Also, judging by the DNA picture in the Japanese logo for X and Y and now the appearance of NewMew, I'm guessing that the plotlines of Pokemon X and Y are going to involve the villains (maybe a return of Rocket or Plasma, but I think a new baddie for the new gen is more likely, possibly scattered remnants of old villainous Teams uniting to form a brand-new evil force) attempting to do something evil by manipulating Pokemon genetics. This would explain the new Breeding quirks, and it could explain the existence of any new Types that may or may not be added in Gen VI. How that would work in with the version mascots, I don't know. Maybe they're genetically altered too.
As for all the mindless fanboy/fangirl rage, that tends to happen at the beginning of every new gen. It's no big deal.