I'm playing it right now. It's a very close adaptation of the board game, so while game mechanics are very simple, it all combines together to become more about controlling choke points and managing risk than about quick reactions and micromanaging individuals.
The core mechanic is overwatch- you have four action points a turn (plus a small pool shared amongst the squad) that allow a Terminator can move, move backwards, or move and shoot, or turn and shoot etc, he can also spend two of his points to set overwatch. This allows him to shoot at a genestealer (think Aliens) if it moves within his line of sight during the alien turn, but at a reduced chance to hit. Every time he fires, there is a slim chance his storm bolter (machine gun) will jam, costing two action points to clear and rendering any further overwatch attacks lost. Not every Terminator carries a bolter, some have melee weapons too or a heavy weapon instead, but 4/5 of the squad are equipped with them so mastering their probabilities of hitting or jamming over however many squares it will take the alien that is lurking around the corner to reach you is key. Also, you can't rely too much on the extra points as they are random, you need to capitalise on them to advance when you have a surplus, but be prepared to go without too.
The campaign introduces all the mechanics gradually (as did the board game), but there are some downsides. Terminator movement is a little slow, and text is now too small in the Vita port- they should have increased it. The upside is that the darkness and visuals are very '40k', all gothic, industrial and claustrophobic, and the map designs are clearly made to challenge the player's abilties to advance and protect their troops simultaneously.
I'd be interested to hear other impressions of this, as with Blood Bowl I'm a bit biased in that I grew up playing the board games and painting the miniatures, so while it seems simple enough and elegantly designed to me, it might seem brutal to someone not used to the random element of a 1/6 chance of a bad result with each shot.