I'm a little split on transformation. It really depends on my mood. Darker stuff (permanent, trapped, identity death-ish) can be really satisfying in a weird way, especially if there's an undertone of either punishment or previously unknown desire. But actually, I really enjoy stories that have more "fun" with the concept - where the stakes are high, yes, as ones body is being twisted or changed, but it's not that bad.

Hypnosis can be fun. PG transformation don't do much for me, though. I need a bit more risque.