What's your favourite voxel-based game?

Every time I play Space Engineers, or even write a post about it, I’m blown away by the recent planetary update. The sheer size of the new playfields, not to mention the fact that they’re all fully changeable by players, is one of the most impressive game industry feats that I’ve seen in quite a while.

I’m curious to see if other voxel-based titles can improve on Keen’s design, and as such I’m also curious to know about the MOP community’s affinity for these sorts of games. Aside from Landmark, there aren’t many playable voxel-based MMORPGs at this point, but what say you? What’s your favorite voxel game in general?

TH