TerraTech - Explore, Craft, Build. Is it as good as it looks?

TerraTech is currently on a free weekend via Steam and on sale for 40% off. It looks great on the surface as a crafting and modular building and exploration sandbox game, with both single and multiplayer modes (though I am only really interested in single player).

Has anyone given TerraTech a good workout? I’ve been in the mood for Lego-type things lately and am wondering whether the execution here stands up to the concept.

Says its on free trial for the next 3 days for me…time to find out?