Post-campaign feedback/survey

[Lord Il Palazzo]

I recently finished up a campaign I was DMing and am looking to send my players an email asking for feedback. Like (I feel) most DMs, I don't get a huge amount of feedback after sessions besides "that was fun", "I'm curious what's going to happen next" or "I was surprised to see that NPC again" and I'm hoping, now that the campaign's complete I can get a bit more. I don't want to be too long about it since the more time it takes to answer, the fewer answers I feel I'm likely to get, but I want to have enough questions that cover enough ground that it's useful for improving the next game I run (for the same group).

What sorts of questions do you think I should ask? The only thing I'm (mostly sure) I'm going to include is a "What thing or things do you think were done well in the game and why?" and a matching question about what was done poorly or needed improvement.

Some other ideas I've got but that I'm not sure about are: favorite/least favorite scene/session/encounter; was there enough/too much/not enough combat/roleplaying/challenge; did you feel like your character got enough focus or had enough to contribute (both in and out of combat); as I DMed, did I communicate what was going on well or were there any places where there was confusion?

What do you think of these questions and are there any others you think I should ask?

[Laserlight]

I asked about the mix of combat / social / explore; favorite combats; favorite encounters; favorite villains.

They wanted:
-- more dynamic terrain--eg, there was a fight on a lake with floating mats of plants, and jumping from one to another would push both of them away from each other.
-- more non-combat encounters
-- more threatening fights--the "best fights" were consistently the ones where someone was down to his last couple of HP
-- villains much more powerful than the party--"we can't defeat him, we can only throw obstacles and run and hope he doesn't track us"