Well, there's not been any gameplay yet, but I think it's easy to understand why fans aren't fond of it. The tone feels totally different, feels like it's trying to go down that edgy, angsty for the sake of edge and angst path. The other games always had this somewhat tongue-in-cheek feel to it, even in the more 'serious' moments, and the trailer just lacks that. And, yeah, the character does look totally different. Sure, it's suppose to be young Dante, but he doesn't even look like that really (the hair isn't dyed, it's a demon thing). Maybe it's before the demon blood kicks in or something, so maybe he'll transform a little, who knows. That, and we've already kind of done the delve into Dante's past thing with DMC3. So, it just seems like a very wonky direction. Unless this is a reboot or something, which maybe it is.
Of course, those kinds of games are basically 90% gameplay, so hopefully that's up to par.