I'm doing this now, but with OMSCS. One class at a time is all I can manage. The program is rigorous.
I've been thinking about doing this, too. Would you say it is interesting and a lot of work or just a lot of work?
It can definitely be interesting, but like any program, it depends on the course and professor. I’ve had some great courses (like the intro AI course I took last Fall) and I’ve had a terrible course (decent relational database course, but the only TA who responded to questions was absolutely terrible to students).
I enrolled in the program because I don’t have an undergrad in CS. I wanted to strengthen my credentials and, more importantly, my foundations. So far, I’d say the program has definitely helped with that. It is also a lot of work, but one course a semester isn’t going to preclude you from having a life. Two will keep you seriously busy though.