I would recommend 'Ghost Light' by Joseph O'Connor. It's a fictional exploration of the relationship between Bram Stoker and the actor Henry Irving. 'The Spinning Heart' by Donal Ryan is a collection of interlinked stories that give a great view of modern - day Irish life. And 'The Butchers' by Ruth Gilligan is a gripping fictional story set in Ireland that deals with themes of family, secrets, and history.
A great one is 'The Country Girls' trilogy by Edna O'Brien. It was quite controversial when it was first published but is now seen as a classic of Irish fiction. 'Tales of the City' by Maeve Binchy is also very popular. It has a lot of heart and tells stories of different characters in an Irish town. Also, 'The Third Policeman' by Flann O'Brien is a cult classic, with its strange and wonderful fictional world.
James Joyce's 'Finnegans Wake' is a very important work, though it can be quite difficult to understand. It's full of wordplay and complex themes. Another is 'The Secret Scripture' by Sebastian Barry, which tells a story of an elderly woman in a mental hospital and her past. And don't forget 'The Sea' by John Banville, a beautifully written fictional work about loss and memory.