I picked up the 3D BluRay today and just got thru watching it. Saw the first half on my 2010 Samsung 3D active plasma and the 2nd half on my LG LM7600 passive LCD.
In terms of the movie itself, I found it moderately entertaining but not particularly memorable in any way. I've seen a couple of the prior Underworld films and this one seemed hamstrung by a low budget as the action sequences weren't nearly as ambitious as those of the earlier films and most of the CGI lycans had a texture resembling rubber more than fur. As usual with these kinds of movies, it ends in a quasi-cliffhanger leaving things open for yet another hoped for sequel.
In terms of 3D, again I found it moderately well presented but not particularly striking. Despite the dark palette there is a moderate amount of depth and the occasional item poking out of the screen. The best examples of 3D involve Selene's encounters with a particularly large lycan and a sequence with silver nitrate particles was kind of interesting visually but quite honestly nothing in this movie really struck me as demo worthy. There were a few instances of ghosting on the plasma in scenes with extreme contrast ranges such as lighted windows in dark buildings during night scenes, pretty typical of early gen 3D plasmas. The image was perfect on the passive LCD.
The film was ostensibly shot with the RED camera system and while it is presented in a letterbox format of around 2.35:1, it's pretty obvious that the cinematographer composed a lot of the shots with 1.78:1 in mind. Heads are routinely cropped at the top in closeups and there's scene early on of a newscaster delivering the news while the text scrolling across the bottom of the screen is partially obscured by the lower letterbox. Even closeups of the CGI lycans lunging towards the screen are often oddly cropped. It would have been better if the filmmakers had just taken off the mattes and left the film full screen as the compositions would seem to have worked better that way.
I got it for $20 at Best Buy and at that price it's a decent deal if you're into the genre; others may want to opt to rent.