Was the web on its own interesting enough in 2000 to make this a killer device?
Yes, it was. Were you still wading on CompuServ and Usenet or something at the time? :)
Also, what OS does it run, can it do anything but surf the web?
EPOC could do lots more than surf the web; it had apps for all the obvious personal-assistant functions (calendar, notes, to-do, contacts) and had a decent ecosystem of third-party apps. It powered the Psion PDAs (clamshells with decent thumb keyboards and stylus input), and was head-and-shoulders bettter than PalmOS or WinCE (its contemporaries) in terms of stability and ability to run on low-power hardware. I nursed one of the later Psions along for years after they were discontinued, until the iPhone came along and there was finally another pocket computer worth switching too. The devices' main weakness (other than nonexistent marketing) was the state of mobile connectivity in their day: slow-n-crappy cellular data, hard-to-find local wireless, and dial-up.