Advent of Code 2019
Many of the comments are about the event as a whole, but I'd like to commend the author for the day 1 puzzle, which I think is very cleverly written. Many people (including myself) use these as an opportunity to try out learning a new language, and the first puzzle does a good job of making sure you know enough basic operations for some of the puzzles coming up. The puzzle itself wasn't very difficult, you could do it by hand if you really wanted to, but it required you to know how to read and parse lines in a file, handle compound data structures, iterate through, and perform basic operations (floor, casting strings to ints, etc). I thought it was really well done, and creates the basic knowledge for the puzzles ahead.