An immediate 10/10 from me.
When I first saw "Castrovalva" I learned just how bad The Master really was, and this episode reinforced it. Simm's Master is incredible, he's funny and totally evil... well, either that or totally insane.
Our heroes are really in a pickle now. I can't wait to see the next one. But what's going to happen to The Doctor...? I thought David Tennant was going to stay on at least another year, from an article I read, but now it looks like there's nothing he can do but regenerate.
Anyway, an astounding episode. Can't wait for next week's.
Oh, and as for Utopia(the place, not the episode), they may explain it in the next episode or it may be shown next season.
Only problem I actually had with this episode was that I can't get that drumming noise out of my head...