Irish Music, in my opinion, can be divided in 2 categories. Irish Folk, or Traditional and Irish Punk/Rock.
Irish Folk normally uses only traditional instruments such as the violin, the acoustic guitar, the accordeon and the tin whistle, although some bands have also started to use the banjo too. The songs are played mostly in Allegro, very fast and lively with plenty of chorus, although most have a set vocalist it is normal for the whole band to sing during the chorus. The listeners are encouraged to beat and sing along to the song too.
This is all in antithesis to the actual lyrics of the songs, which most of the time talk about sad things, most commonly the need to leave Ireland because of basically the British. Examples of such songs would be The Black Velvet Band and Poor Paddy Works on the Railway. I couldn't find a good example of Poor Paddy on YOUTUBE but here is the Black Velvet Band:
Black Velvet Band - The Dubliners([youtube] doesn't work helpo)
To summarize, the Irish fucking hate the English. Maybe I will talk about Irish Punk/Rock someday who KNOWS.