I've been doing it in Scheme this year, as a major branch of the LISP family I've never tried before. Super-impressed by the speed and solidity of the Chez Scheme implementation, but still a little undecided about how much I like Scheme for day-to-day use. (After Clojure, both Scheme and Common LISP seem to have a fair number of "why is this taking so many keystrokes?" moments).

I know a number of people thought some of the "simulation with lots of details to keep track of" problems were a bit over the top this year. Personally, I rather enjoyed them, and in particular found day 15 really satisfying to complete. Not something you'd want to do every day, but it's good to have some problems which pose a bit of a challenge without turning into a "can you pattern-match this against an algorithms textbook" exercise. The overall breadth and balance of problem types was impressive as ever.

I hope it's back next year!