Until April 11th, Legend of Grimrock can be pre-ordered from the http://www.grimrock.net/ (gives you a Steam key and DRM free copy on release) or http://www.gog.com/gamecard/legend_of_grimrock, for 20% off from either site. That's 12 dollars/9.1 euros. http://www.rockpapershotgun.com/2012/04/04/wot-i-think-legend-of-grimrock/ was very positive about the game, as was http://www.youtube.com/watch?v=dzIiXx-8BHc in his video.
At that price, if you have any interest in the genre, that seems like a no brainer.

If you want it on Steam, pre-ordering a copy from the dev's site would be the best thing to do since it's going to cost you less, and the devs probably get a larger cut of the money when you buy it directly from them instead of through Steam.