Well it was my first low level experience so a lot of it was new to me - I hadn't even used C before so pointers alone were a revelation of sorts. I was blown away by the idea of interpretation and then once we delved into forking and processes (and zombie processes), well I truly went down the rabbit hole. It was really cool implementing your own system hooks with Minix - being able to press F12 to get a formatted tables of all running system calls was supremely satisfying. I fully appreciated how complicated and yet in a way beautiful OSes could be and it forced me to learn how to sweat the small stuff and build good software from the ground up.