I took both classes, but I really didn't care for Reactive as much. The first Coursera class really turned me on to the elegance of functional programming with Scala's unique type system, but much of that elegance is really lost dealing with some of the structures introduced in the second class, in my opinion.
Reactive is split into three "subclasses". The beginning part, taught again by Odersky, was a pretty useful extension of what was taught in the first class. As with the first class, the lectures were very well thought out. Although, some of the examples abandon the beauty of side-effect free programming, which was a letdown after really being turned on to that style in the first course.
The middle section on Futures and ScalaRx was pretty rough. Those lectures, done by Erik Meijer (I believe), were less clear and less well planned. I don't know if there's an impedance mismatch between Scala and the reactive style or if ScalaRx is just the wrong abstraction, but the joy of Scala was completely lost for me in these two lectures. I'm used to Javascript's Promises/Deferreds, which are essentially the same thing as Scala's Futures/Promises, but the former are far more intuitive syntactically.
I did, however, find the final three lectures on Akka to be very well taught. I had no experience on actor model programming, but I came away very intrigued by the possibilities.
A complaint that spans all three sections was that the assignments could be better focused on the the concepts at hand. Each can require a fair bit of constructing your own test and debugging frameworks to figure out how to pass the rather opaque and unhelpful automatic grading system. I eventually lost patience and quit doing the assignments after floundering with the tools.
I concur. I loved the Functional Programming Principles in Scala course and recommend it to everyone I can. However, I'm not at all sold on the Reactive Programming course.
Erik Meijer's lectures -- at least in the first iteration of the course; maybe they've gotten better -- were riddled with errors, confusing exercises, and an overall lack of coherence with the rest of the course. It pains me to say this because Erik seems like a cheerful guy and I really wanted to like his lectures, but they are a mess.
Even Roland Kuhn's lectures, which are pretty good and a lot clearer than Erik's, didn't manage to sell reactive programming to me. One glaring problem was that the actor model seems to throw away most of Scala's static type checking, which we had learned on the previous functional course. Suddenly it's ok to pass whatever message to actors in a way that seems closer to dynamic typing.
I've always found this to be a strange duality in the Scala community. On the one hand they praise strong, static type checking in general Scala programming, and on the other hand they praise an almost untyped paradigm in the actor model. And few people seem to take issue with this.
I did start that course, but after the first 2-3 videos I couldn't find the time to continue working through it. Back then I was working on a customer project that required a lot of attention. I may want to try it again the next time that it is being offered.
It's also by Martin Odersky, but also with Erik Meijer and Roland Kuhn.
https://www.coursera.org/course/reactive