I rebuilt Tetris in Godot piece by piece and of all of the classic arcade games that I've programmed it was by far the most demanding game. the specific randomization rules (did you know that the original used different randomization from the one on the Nintendo which uses different randomization from what's standard now? I do!), sliding, T spin detection, copying score tables and combo tables, input buffering and DAS and so many more little things that I've forgotten about, it was a nightmare but it taught me a lot.

Partly what makes it so difficult is that there's so much expectation around Tetris that there isn't around, say, Space Invaders. if you just made a straight one-to-one recreation of the original Electronika version people would say that it is barely functional and sucks. so much of the game that we consider Tetris is essentially patches that have been applied to the base game over the past several decades and it's many many re-releases.

it's one of the purest expressions of "video game", I absolutely love it. 10/10.