Thanks for the replies.
How would you approach this situation:How do you ask for specific answers without sounding judgemental or critical?
Bullgrit
How I normally do it ...
After every game session, we usually have a follow-up email with brief recap and XP (I don't like giving it out during the session in case I need to adjust some things with more time). So that email usually allows for an open door for people to send general comments.
However, I (personally) would never purposely ask specific questions.
I don't want someone to think i'm picking on them, and, really there shouldn't be a right or wrong choice in RPGs. If I start asking specific questions, I do have to worry about how the players will view it and I don't want them second guessing their free will to go right/left at every corridor (that's an exaggeration but just trying to illustrate an extreme of my point).
Having said that, how I would approach it (presuming no one decided to jump in on their own with comments) ...
1) While it is still fresh in minds but not immediately (so maybe a couple days later, but not a week later), I'd make sure no one was _upset_ so a general email question like "Is everyone okay with how things played out? Does someone feel that dm fiat should be introduced to alter what seemed to be the end?" (that type of thing -- note i don't ask about specific choices that were made, just making sure that no one is upset by the game's resolution and if there is a valid argument (i.e. some unfair ruling) that should be reversed.)
2) _Maybe_ after a while has passed and people are at the point where you think you can make passing comments/jokes about it, just toss it out there "just curious - in that campaign a month ago, why did you guys decide to jump off the cliff back then at the end?"
... but that's just my style and what i know of my particular set of players...

your style and the needs of your particular players may be different...