Finished this a few months ago. I read Disgrace and Diary of a Bad Year before this. I prefer this and Disgrace to the latter.
Overall, I was impressed with Summertime. It is another example of Coetzee midly taking a stab at metafiction, which is one way to describe his last three pieces of fiction. The interviews, some more than others, are captivating and intriguing. I enjoyed his depictions of women. Sometimes I think he overdoes the image he is constructing of himself: negligent, arrogant, selfish, inept, blah blah blah, but it's a courageous thing to try.
It's altogether an "odd" book, I think. The influence of Kafka and Beckett are palpable in the prose.
Other than the interviews, the book begins and ends with journal entries. I wish he included more of these, and perhaps spread them throughout the book (maybe between the interviews), instead of only having them at the beginning and end.
It's a quick read, so definitely read it if you have time, and especially if you're familiar with Coetzee's work.