Nah, it's not the worst game mode ever, but it's hard as hell (hardly surprising, it IS the hardest difficulty level in the game). Here's some advice (though you probably won't need it all) :
- play with friends only, with mics if possible
- Swamp Fever is, by far, the best map for this. You might want to avoid running crescendos, as camping is easier than running around while fighting hordes of zombies. SF is the only campaign without such crescendos, and the finale is pretty easy if you camp in the stairs on the right side of the house (when facing the escape route).
- make sure you can finish each and every campaign on expert with your friends before tackling expert realism. It's a pre-requisite, you need to to get used to expert. That way, you'll learn to avoid shooting your friends by mistake (which is crucial in ER, since you can't see your teammates glowing)
- always save healing items for when you really need it. Except in rare case, always save them for when you're black and white. When Black and White, ALWAYS heal straight away if you got a medkit. Never stay in such a state if you can avoid it. If there's not kit, ask your friends for pills/adrenaline.
- learn to recognise the sound cues when Special Infected are spawning (so that you can anticipate their attacks)
- don't be afraid to explore for items, but don't linger too long, you need to keep moving.
- try to save pipe/molo/bile for events/finale at all costs
- lots of other advice
- always make sure you only use the defib as a last resort measure. It is, after all, the only items, with medkits, that can make you go back to green health, so it's better to save it for last. Then again, as with medkits, you need to find the right time to use it, it'd suck if the whole team was swiped out because you were holding out on the kits/defib. It'll come with experience and lots of trials and errors.
Here, I don't know your level or anything, so there's probably stuff you already know/are already doing, so I hope I didn't came across as patronising or anything xD
Oh, and good luck in your endeavour

I'd gladly help you, but I haven't played ER in a long while, so I wouldn't be any help unfortunately...