Professor Cannon is, in my opinion, one of the best educators I have experienced in my entire life. He is very very knowledgeable about the subject. But he is also able to transmit that knowledge so that his students understand it. He explains clearly, succinctly, and well.
Cannon is always available in his frequent office hours, and the TAs (of which there are about 20, and all of whom are amazing as well) also have office hours every day (including Sundays and occasionally Saturdays).
You get 120 hours of "grace time" in the Spring semester (I believe it's 150 hours in the Fall). You can use all, none, or any amount of this. TAKE ADVANTAGE OF IT. It is an incredible resource to have.
As for the workload: I had very minimal CS experience coming into this. However, I've still managed to understand everything he talks about because the man is a supremely good lecturer.
If you have the opportunity to take a class with him, do not under any circumstances switch out! It is worth changing the rest of your schedule to accomodate his class.