Light rail in Dublin is quite good, but coverage isn’t great. I used DART a few times, and it wasn’t a nice experience - long waits and less than ideal trains. I traveled by rail between Dublin and Cork, however, and it was quite good - modern and comfortable, and relatively fast (Ireland is small and fast rail feels like overkill)

Not sure I'd say that; a modern TVG/ICE-type service could do Dublin to Cork in less than an hour, vs 2.5 hours for the current service. That would be a game changer.

There are vague plans for such a service, and more solid plans for upgrading to 200km/h (the trains already support this but the line would need upgrading).