I quite liked it 25 (!) years ago
One of my first companies after graduating used Notes for email, “groupware” and chunks of their intranet by publishing NSFs online via Domino. I mostly interacted with it as a user, not an IT bod.
As a mail client it was… alright. Kind of a clunky UI (we were on v4 I think) but a step up in features from Eudora or whatever I’d been using as a student. A couple of years after I joined they replaced it with Outlook, probably instead of moving to R5.
The groupware stuff hung round for a while though. In fact that place had the best corporate document management system I’ve ever used, and it was built on Domino. We also had issue tracking systems, distributed file stores that used the underlying replication technology, all sorts of good things.
It always felt to me like a product that missed its true calling. The vision was great, but people didn’t see it or couldn’t get past the quirky UI. Or, maybe, they couldn’t get past the cost. Intranets and web technologies eventually put paid to the groupware, and Outlook/Exchange killed the email side.