I understand that some folks didn't care for USM. To me, it hit at the absolute right time.
I'd given up on the 616 Spidey titles and was bummed by the direction they were taking at the time. Then Ultimate hit, and everything worked for me: Bagley's art, which I'd always loved, a new continuity, but most of all, teenaged Peter Parker written in a smart, snappy, and relatable style.
Bendis became one of my favorite writers, and I still think his best work is with teenaged characters. Never before had I laughed out loud so many times when reading a comic, while also being moved.
I'm also in the middle of re-reading the issues. The series works best overall in collected form. There's a great rhythm and pace at work that you miss with the monthlies, which I collected and always read first when new comics were released.
I'm sorry to see that Peter Parker is gone, as I personally think the 616 Spidey and his status/world is a disaster. I'd return to the book if Peter was brought back and Bagley returned, but since that's not likely to happen, I at least have the back issues.
Bendis and Bagley's USM was more faithful to the heart and soul of Peter Parker and his world than the 616 stories have been in a very long time.