I played around with this a little with a friend thus afternoon. A couple impressions:

1. The voice chat / positional audio works very well. I was impressed.

2. The world is too vast for the current user base. It felt like a ghost town and before my friend joined I wondered if it was broken. There was a 60 on the screen, but there was no one in the rooms. Based on the chat history a lot of people had that experience.

3. Is this federated yet? I couldn't find an option to log in with my own homeserver account. If there was such an option is there a way to make it less scary - every matrix integrated game / tech demo I've seen that uses my account wants me to enter my password in their site and that feels wrong.