I love this. It's greatly animated and the artwork is awesome. As for the story, it leaves so many open ended questions from logical ones (as "if the door was closed when you got in, how did it open to let the cat in?") to more phylosophical ones like "What does the second key open?" and " who else is there?"
Also I just finished the last televised saga of Bleach (anime) and in it there was a girl with the power to put anyone she wanted into any container she wanted until she let them out. She onced kept the neighbour she had a crush on in there until he rejected her very being. She calls this power "Dollhouse". So questions reflecting this also buzz through my mind.