While I'm def excited about this game, when I thought about it, how is this not just the second half of Second Life by Linden Labs? Second Life already offers an MMO with object creation (Minecraft) and scripting (0x10c). While the sci-fi story line is more appealing to me, the concept of building thing and coding their workings in a 3D MMO doesn't seem novel to me... Unless I completely misunderstood something.
Execution counts. A similar concept doesn't guarantee a similar user experience.
Notch is talking about real resource management issues, combat as an inherent part of the game, random AI encounters, etc..
This is a game that happens to share some SL-like properties. SL is just a framework. Arguably that makes SL more interesting in some ways, but it's also a lot harder to "get" something out of SL other than pure socialization.