Ughhh!
Started using Lotus Notes before they were taken over by IBM, back when the only supported server platform was OS/2. It was used in-house for running various internal databases for the support, sales and admin departments, and we also did some development work for elsewhere.
My general experience was that it was fine for certain types of database which required just a few users, but bad for implementing E-mail; the latter confirmed by discovering the arcane process that ran nightly to purge attachments from deleted E-mails.
At one point my workplace developed an intranet produce that used the web-server component of Notes to serve documents internally, with a few third-party libraries thrown in for document conversion. The Notes web-server was singled threaded back then, and the search mechanism, whilst thorough, was somewhat slow, resulting in the server being potentially unavailable for minutes whilst handling a search query.
I can also recall other quirks, such as embedded Word attachments gaining the page dimensions of the form that they were embedded in when printed, which caused no end of fun with some printers.