Insanely Twisted Shadow Planet
It's pretty fun! The presentation is stupendous -- a dark art style, mostly-vacant soundtrack, and finely tuned camera movement really reinforce a sense of foreboding tension in the bowels of the Shadow Planet. It nails the feelings of isolation and exploration that most Metroid-likes shoot for, and ITSP's unique features - upgrades like a grabber claw and a buzzsaw - really differentiate it from its inspirations (unlike, say, Shadow Complex).
I do have one big concern though, in terms of game length. After a little more than an hour I'm already 32% of the way through the campaign (and have 34% of the map explored). Given the game's pace so far, I don't know if it can really blow me away in the next 2-3 hours.
Progress: 32%