We took the train once from Dublin to Galway. I wouldn't do it again...all you could see from the train were tall bushes, trees and peat bogs. There are trains and there are trains. I would say that in other countries you get great scenery from the trains, but maybe not as much as you expect in Ireland.

This one, however, looks good:
http://www.docbrown.info/docspics/du.../dspage08a.htm