The notes are all very good. I also have a copy of the NIV Reformation Bible and the notes and other extras are better in the NIV than the ESV Bible. Also, the NIV includes the Westminster articles, the Canons of Dordt, and more that the ESV does not. If you are already familiar with these documents, I wouldn't worry so much about it.
If the ESV scripture was inserted into the NIV extras, the total package would be (IMHO) ideal. As it is, if you are well-versed in Reformed theology (I know you are) you may want to consider getting a more basic Bible. I love my Reformation ESV Bible, but I don't have a background of knowledge like many others in this forum. The chief end of man is something I had never considered until a year or two ago, and that was from reading "Desiring God" by Piper, not even a PCA pastor! I need the notes and am learning as I go.