Given how little we know about Landmark's details, I'm a little leery of dedicating too much time to it. The building part of Minecraft is the least of the enjoyment I get out of it. What I have fun doing is funnelling mobs into death chambers, creating automated farms, complex piston contraptions, hopper and redstone circuits. If Minecraft was just a game of building large static structures... I definitely wouldn't put as much time into it.
With the size of the voxels, it would make it hard to do rails I imagine and I'm having a hard time imagining how they would implement pistons (or something of the like to move voxels around without players in "edit mode"). With the confined "building plots", I think it's going to be hard to do large scale mining operations or get into machinery like some of the mods add.
They also said they want to allow people to build Sci-Fi environments, but without some way to program the voxels or some kind of complex mechanisms... it's only going to be people making non-functioning ship husks and getting bored.