Specifically CS7210 is demanding because of its assignments. The assignments come from UW's CSE452, have very little direct connection with the course lectures, and require you to implement a Paxos-like system correctly, basically in one shot, in an environment that is very difficult to debug. So the projects turn into 60-80-hour slogs where students change parameters semi-randomly until something starts working. CS7210 shares that aspect with a number of other courses in the program.