I tried it back in 2004, and the thing that struck me most about it (besides the fact that it was free) was the speed. It took FOREVER to open and save. I was in a phase when I was trying to move over to as much open source software as possible to save money, but OpenOffice just ended up frustrating me. Also, I recall fighting against the program to do simple things in spreadsheets.
I use and love Gnumeric now for spreadsheets, but I resolved that I'd rather pay for MSOffice. It isn't perfect, but I was willing to pay.
I was always so confused about it too, because my initial exposure to open source taught me to expect this kind of software to, as a rule, always be leaner, smaller, cleaner and faster than "bloated" MS products, but I walked away from OO feeling IT was more bloated.