LEGO Universe, failing partly because the 'dong detection' software part of it proved amazingly expensive, just got a single player version in the shape of LEGO Worlds. I didn't even know about that project to my own shame, as this is something I've always wanted to see and have, and now I don't know whether to be happy or sad, though I'm thinking mostly sad.
Anyway, this sounds like the next best thing. Released on Steam Early access right along with the first announcement of the title is a nice surprise and can become an interesting trend (we've seen it happen a few times now), and it was a no-brainer for me to get immediately, considering that my son is just starting to get into Minecraft and is a complete LEGO nut.