It's been over a decade since I read Operating Instructions, so I can't really weigh in on the comparison. I remember OI really blowing me away, which this one did not, but I also think I was somewhat easier to impress with books back then. At any rate, this was a good book to read as I prepare for a new baby in my own life, especially because it gave me some good insight into the "grandmother" and "mother-in-law" perspective. I think Lamott presumed WAY too much control over her son and his girlfriend's choices when it came to their child, and I hope she didn't come across quite so controlling in real life as she does in the "privacy" of her journal (that she knew would be published.) Grandparents in the delivery room, her thinking she had any say over where the baby would be baptized, etc., all went way too far in my opinion. Although her son was young when his child was born, in some ways that might be all the more reason to back off and make sure he and his partner could find their own way.
At the same time, one can hardly hold someone's feelings against them, and I try not to judge memoir by the foibles or personality of the author unless she is super immoral or obnoxious, and Lamott does not rise to that level -- she is just letting her weakness and her humanity show. I love reading published journals, and this one may have been slightly self-conscious because she had a contract for it as she was writing it, but it held my interest nonetheless and also reminded me to try to be a better journaler myself.