This class is a grind and a half. I hope you're good at math because you're going to need a lot of it. Most of the first unit is combinatorics and statistics, with the following units being more focused around taking integrals and partial derivatives. The textbook usually goes into way more depth regarding the mathematical derivations used in the class than Tim does, so it doesn't hurt to just skim them (as long as you know the physical meaning of what the math is telling you, Tim is big on that. As far as the lectures go, Tim is a fantastic lecturer. He knows how to keep the class engaged with rather dense material and can answer practically any question you throw his way.
Workload is fair, but expect to study a good amount. There is a weekly problem set posted, with 3 or 4 of the problems each week to be collected and graded. Make sure you give these the time of day because it's an easy way to get a good grade that's worth 25% of the total. If you want to do well on the final, however, it's a good idea to go through all 10 or so problems posted on each problem set. On one exam, he slightly altered a question from the textbook that wasn't included in the problem set, so going through extra problems can only serve to benefit you.
The midterms (25% each) and final (50%) were difficult, but fair. Averages were usually around the 70% mark. Time management is usually the limiting factor; no one every finished their exam earlier than the allotted time (including the 3 hour final). If you went through the problem sets diligently, the material should all be familiar, Tim wasn't one for throwing complete curveballs. He also is generous with partial credit, so even if you can't show all of the math, he usually grants points if yo can explain with words the concepts.