I think this is what Notch wanted for Minecraft in someways (though I'd guess he's happy with MC as it is)- he has said many times that he wanted a RPG game- minecraft grew because of it's creative elements more than it's RPG elements, this isn't a bad thing really its a fun game regardless...
This game [CubeWorld] is really well thought out and I think anyone who enjoyed older RPGs like Diablo or Zelda will enjoy it. - It's got a great mix of elements from the classic games that really have shaped this genre.
YES it is Voxel based- but it is NOT in anyway a Minecraft clone- there is very little manipulation done to the environment, the terrain generation is a lot more lively, there is more scripting and less generality in regard to AI.
It has a more traditional quest/leveling system that binds your characters "power" (overall damage output etc) to your level (basically) - as you level you get more powerful. I know MC leveling can make you more powerful- but that comes down to items and "magic" wheras in CW your character "grows" over time.
I will also say that it *feels* like a much LARGER world that minecraft- you cross country "boundaries" and encounter different Biomes at much farther intervals, and the map gives you a better idea of what's happening than in Minecraft (which is more survivor man in this regard).
Sure you could say "Oh MC could do that with mods" - but the point is that is hasn't- and likely won't. This game has smooth fun combat, cleanly generated worlds, smart and tactful AI, crafting, skill trees, a nice leveling system and a VERY believable environment (kinda like how Skyrim gives you that, Wow this place looks legit feeling once you get past the voxel part hah), a huge list of pets (some of which can be mounts), loads of different weapon types, class types, and fighting styles...
All of this after 2 years and two developers - And it is in Alpha.
As much as I love MC, this game is FAR more polished in its early Alpha stages than MC has ever really been- sure you could fire up MC and run it smoothly now, but it's lacking a lot of HUGE features that CW has right of the bat as core gameplay elements. MC is a "create an adventure" game where as CW is more flat out- "adventure here" game.
Nothing against either of them- they're totally different, just been having a lot of fun in CW as it stands- COOP was a blast w/ my g/f right out of the box.