I went into Katherine's class annoyed b/c I was expecting Matty to teach and there was a schedule change. I have to say, I was pleasantly surprised b/c Katherine was awesome. Great energy, good timing on the intervals (she ran a little short on the sprints, etc. but I way prefer undershooting than over when I'm dying on the treadmill), solid music, and really a lot of fun (and she was rocking kind of amazing capri workout pants with sheer mesh panels that were reminiscent of Madonna circa Vogue tour that were very inspirational). It wasn't the hardest Barry's class I've ever taken, but it was consistently challenging. We did a 16 minute interval on the treadmill, which I'm a fan of b/c I feel like you can get a little mileage in rather than running for like 7 minutes and hopping off. Lots of side shuffling and skipping, which is a nice way to mix it up. I was super into the floor sessions b/c I thought everything we did was very "doable", whereas sometimes during floor I'm like a pathetic puddle (literally and metaphorically) of exhaustion and have to keep stopping. Katherine's floor sessions were well thought out and I could do the whole thing without taking breaks--which made me feel like a badass as opposed to an out of shape slacker. I think 5 stars should be given very judiciously-- basically only to classes where one feels like it was well worth it to set your alarm at midnight so you can be assured a spot in class by being online to book exactly when the window opens (for the record, I have never done that, but evidently, according to the folks at Barry's, lots of people do)--but Katherine's class was really great. I would definitely take her again and be psyched about it.