Yeah, it's good. It gets very challenging once you are fully into the game, and the mechanics of the earth, water, and lava all interact seamlessly. Definitely worth the price tag!
The only (semi)-major problem I have with it is that, more than once, I'd accidently pick up a tiny pool of water I never saw rather than earth, and then get confused why I suddenly couldn't do anything (a pool that small doesn't show up when it's been picked up). It nearly cost me big time on the 2nd to last map.