Have to say, being Irish, I've never really been exposed to it (didn't even know it existed until I was fairly late into my teens and I was raised in a rugby-mad household). The few bits I have watched have never really grabbed me but I've never watched a full game at the same time. I do say this appreciating that all I've ever seen is bits of a few lower of the lower quality games at the last world cup and the odd highlights show some random evening of some games in the English league. Never seen the NRL or anything which as I understand it is at a much higher standard so entirely possible I don't know what I'm missing out on.
I'm not particular well informed about the rift between Union and League but it does seem pretty petty/bitter from both sides, neither seem to have covered themselves in glory over the decades and instead of a healthy rivalry or banter, the mud slinging does seem to have genuine hatred and animosity behind it (although maybe that's just a symptom of a wider rift in England society, like I say I don't fully understand it and will happy accept anyone more familiar with the issues' opinion over mine.)
At the end of the day it's never been worth my while trying to get into it, no emotion connection to it at all and no readily available content means it's very far down the list of sports for me despite some similarities to my favourite sport.
Will say that League, Sevens (especially) and most other variations tend to just be union with all the stuff I like taken out some none of them have ever really been for me.