This was also my experience. It's also been one of the few games my wife has played intensely. We both got quite bored of it after a couple of weeks of addicting play. It's a really great concept, just severely lacking in any overall goal. Makes me wonder what a dedicated, complete minecraft-like game could accomplish.

It's also an excellent example of getting a working prototype out as soon as possible. You never know, it may be even more successful than the completed version. :-)