The good: Nice exercises for beginners. Tab-completion, accepts readline characters like ctrl-u.

The bad: You don't see the (wrong) output if you don't get it right the first time, making it hard to work iteratively and having to guess what the question actually intended.

E.g. 'Seven files that start with "Santa"' actually wants file names that start with Santa, after some questions that had you use "grep" to search file contents. Where I actually struggled with what's expected is Day 11.

The ugly: Actually a very nice design.