Yea, I started reading it a little while ago, and right now I'm on his review of book four.
I kind of have mixed feelings about it, I mean I love his reactions, and I love being able to read about someone becoming a fan as it happens, but to me he seems kind of ... slow at some points.
Like in PoA when they were explaining about Pettigrew and he was so confused, and he was talking about it for like 5 chapters, and then was still asking "wait so Pettigrew was working for voldemort, not sirius black?" And like in one chapter Lupin says "of course I know how to work the map, I'm moony, it's what my friends called me in school." then the next chapter mark is flipping out because he realized that they were the ones who made the map, and I was just like "...umm you didn't realize that when lupin said he was moony?"