The image quality holds up very well considering the approach Cornish and his DOP took towards the film's deliberately comicbook-style aesthetics (as he admits in the documentary 'we went to great lengths to light the film with a view to crushing the contrast in post production'). Due to this, it's not always the most intricately detailed hi-def image you'll ever see (shadows and other areas of black - such as the creatures themselves - are as deep and inky as they come), but it appears to be true to the source material, and that's the whole point of Blu-ray as far as I'm concerned.
The DTS-HD MA 5.1 audio is even better. Plenty of tight, solid, impactful bass accompanying the creatures' footsteps, excellent dialogue clarity (a good thing too for an oldie like myself given some of the accents on display), plenty of creative use of the surrounds (especially in a scene involved a smoke-filled corridor) and wonderful tonality in the music. However, I didn't bother checking out the LPCM 2.0 mix, so I've no idea how that holds up in comparison.