I'm English living in NI and beyond the VERY OCCASIONAL jest made in good humour by someone who knows me well, I've never experienced any anti-English sentiment. My Northern Irish husband, however, was subjected to jokes about his Irishness (potatoes, terrorism, farmers etc) on a daily basis when we lived in England, and still does from some English friends. He's very good-humoured about the whole thing but honestly, the difference is stark and moving here made me realise how unwelcoming it must have been for him when he first moved to London. Whereas I've never experienced anything like that in NI.
NI isn't a small-minded place - in fact I've found quite the opposite, that people are much more willing to accept difference than anywhere else, although I think this is a legacy of the Troubles so wasn't necessarily true twenty or even ten years ago. However it is quite an inexperienced place when it comes to diversity - majority white, English-speaking population etc - which can lead to some backwards attitudes. However, most people I meet are very open to having their attitudes challenged and anything that seems bigoted is usually only due to ignorance, not malice. No different to areas of England with majority white populations in my experience - in fact, more open-minded in most cases.
As for Catholic / Protestant - well, there's still an 'old guard' who feel very vehemently about it, but it's definitely dying out and on a day to day basis, unless you live in a very hardline community, it's not really a massive deal. My (Protestant) niece goes to a Catholic school and her (Protestant minister!) grandfather happily goes along to, and is made to feel very welcome at, her school masses etc.
It's not the same place it was ten years ago - my husband says the same - and I'm very happy to be starting a family here. It's not perfect, but nowhere is, and in the meantime the fantastic education system, the good house prices, the growing economy, the community spirit, the pace of life, the stunning beaches and countryside, the great arts culture etc etc more than make up for its shortfalls. I'm happier here than I have been anywhere, bar London.