By in large it s the fastest way to travel around Ireland, although the network is not as extensive as the main bus network. There is no service at all to Donegal and no north to south routes along the western coast - the Dublin to Belfast route is also the only direct link between north and south. Although your travel time will be cut significantly by taking the train, it is a bit more expensive than travelling by bus.
Tickets also tend to be cheaper midweek and there are often special fares worth enquiring about.
For those who plan on doing a fair amount of travel a train pass is well worth looking into. Irish Rail have an 'Irish Rover' ticket that s valid in the Republic and the North. The ticket costs IEP90 and is valid 5 days out of 15. The 'Irish Explorer' ticket is a combined rail and bus pass, and a handy option considering the limitations of the rail network. Covering all intercity state and private rail and bus lines in the Republic, this ticket costs IEP107 and is valid 8 days out of 15.