I had Fascinate and Razr M and both had deep black levels with flawless albeit non-HD screens. The Maxx HD on the other hand was visibly brighter, not quite at the level of an LCD, but not deep black either. What's worse, there are dark blotches visible on the screen where the pixels actually do turn off like they do everywhere on the M and on the Fascinate. It's only visible on pages with partial text like end of chapters, but still it's there.
I tried to find some technical explanations on what causes this problem and whether companies like Samsung and Motorola (if moto makes those screens) are working on it, but didn't have much luck. I guess it's industry secret at this point. Whoever can get an RGB grid layout with perfect darkness on these screens will have quite an advantage.