Well, firstly they are using LLU or whatever which means their service doesn’t depend on Eircom lines.
Secondly, they offer 2megs for the same price as most of the others offer 512.
Thirdly, if you register within the 1st 100k people you get free line rental forever.
Fourthly they don’t “contend” the network, which apparently is good. :p
Fifthly, they don’t have any upload/download caps per month.
There are probably more reasons why their offer blows the pants off the rest but in all fairness you couldn’t make broadband in Ireland any worse really! ;)