Being male I can't really help on the matter, except to relay what my ex- told me about her own experiences after we broke up (we broke up amicably, but in hindsight this may have been her revenge...).
For her it was not a pleasurable experience, but not uncomfortable either. I would definitely talk to your boyfriend about it first and make sure you feel comfortable. Also lots of lubrication - she told me (and this is the point where the squeamish might turn away) that her boyfriend had "slipped it in" without warning her and without lubrication. Which was bad.
Personally, it's not something that particularly interests me.