There's just not enough information available yet.
At this point anyone claiming it's the second coming of the 360 who is not actively involved in the commercial development of some genuinely revolutionary game or piece of software is just cheerleading for MS.
By the same token, anyone saying it will be a complete flop is likely just projecting their personal wishes.
It could go either way, and even anywhere in between. As in moderate success with continued support, but hardly the game changing revolution initially hyped during the E3 debut.
Worst case scenario would have it ending up like the PS Eye with minimal support although I don't see this happening between Natal integration with Windows 7 as a user interface, as well as MS essentially banking on Natal being a commercial success.