Blockland's an MMOG. It's Massively-Multiplayer, it's online, and it's a game.
In my perspective, when people tell of games with MMO as a genre, they generally mean that the massiveness comes in effect in a single server, with thousands of people in that one server.
Also, if you play WoW, why the hell do you need another free mmo? also what kind of mmo? futuristic? fps? platforming?