Earlier quoted context omitted.
Yes, props to the developer for what they've done, but I am perversely disappointed that this isn't actually a complete OS - process scheduler, file system, TCP/IP stack, multiple user support, all the rest - that only runs Tetris.
I used a few operating systems that were considered "complete," in their time, without a TCP/IP stack or multiple user support. Come to think of it, I don't think they had process schedulers either
(You'd have them in userland. Whether you count that as part of the OS or not, is a different question.)