I have had the misfortune to travel on the Normandy in the past. It was very hot and noisy in the cabins. I would agree with other posters that Irish Ferries don't have a clue. When I am going to France again I will try BF, after the Normandy anything would be an improvement.
I travelled on the old Irish Ferries boat to France last summer. It was a pretty grim experience, but I must say I found the staff to be very friendly and courteous.
I'll be on the Oscar Wilde in a couple of weeks, will be interested to see the difference.