Let me start by being honest. I thought this piece was by far the most difficult and hardest to understand piece in the project. I didn't understand nearly enough of it. I was able to follow the first two third of the first book and very little after that. I'll have some things to say on that part, but I really can't comment on the rest.
My wife teaches math in elementary school and she seemed interested in the things I was reading. However, this is testing time of year so she couldn't really jump in with me. It's possible that I'll come back and hit Nicomachus in more depth this summer.
Another stumbling block is that I don't have a very good head for math. This feels like something of a cop-out but experience has shown it to be true. I'm quite good with kitchen math (adding, subtracting, multiplying, dividing), even to the extent that I can give fairly trustworthy estimates of figures without breaking the numbers down. Where I fail is in the very abstract stuff, which unfortunately is well represented in 'Introduction to Arithmetic'.
I also have trouble with math when I can't see the goal of it. I know that even the parts of it that seem the most impractical have led to real breakthroughs and important things. But this is an area where my mind wants some concrete resolution. In school I had trouble with Algebra but really excelled in Geometry.
Anyway, mea culpa, mea maxima culpa.