Okay, so I picked up the Wii U version for $5 at Wal-Mart, thinking it couldn't be that bad. And I guess it isn't...? But it's not good, either.
It's got a noticeable amount of input lag during any time the framerate drops, which is really, really often. And what's worse is that instead of plain ol' dropping frames, the game seems to slow down. Reminds me of old school SNES slowdown, only obnoxious instead of charming and quaint.
And, is it just me, or is it actually pretty difficult on normal? I consider myself a character action game veteran, but I'm having a hard time on normal. Between the input lag, the hyper aggressive enemies, annoying encounter design (waves after waves of doods, with rocket launcher guys at the periphery), and losing Ryu in a sea of gray soldiers, it's kind of kicking my ass. I've beaten the original Ninja Gaiden on Xbox, and I don't remember it throwing quite so enemies at Ryu at once.