The demo was ok, I'm getting the game just because I've played demo's before that I didn't enjoy, that ended up really good (GRAW, even if I'm rubbish) and some demo's I loved and hated the game (Dead Rising).
Lots of people love it, and it looks amazing, so, give it a go if you can't find a game you like.
Personally, I'd get Gears of War, Viva Pinata, PGR3, and Oblivion before I got Lost Planet. But I have them all so... I'm getting it.