The game is in early beta right now, but it's been in development for years, so the gameplay is very well polished. The best way to describe it would be like a non-collectible card game, or a digital board game, with elements of Starcraft, Magic: the Gathering, and Dominion. You build an economy and develop your board from a pool of units which are partially randomized at the beginning of each game, and new units are being added all the time.
Here's a video that teaches how to play somewhat:
Subreddit which is pretty active: http://www.reddit.com/r/prismata
Check out some player streams (including mine!): http://www.twitch.tv/directory/game/Prismata