I was/am impressed by the lava monster, but the art direction of everything else is second rate, and the real time footage was especially dissapointing. But the way I look at it, Metroid Prime was pretty unimpressive both artistically and technically when Raven Blade was cancelled. So with the right motivation and design help from Nintendo, it could have been pretty good.
As much as I love Metroid, Nintendo needs to give the franchise a rest for a while. And I'd be very interested in seeing something else from Retro.