Yes, as is most cruise lines.
Did you know that nearly EVERY night aboard the QE2 is a formal night? We recently sailed on her for 23 nights and 21 of those were formal nights! That ways too much I think, but regulars aboard her seem to go for that. The NEW formal for a man is a dark lounge suit or dinner jacket and a fancy ordinary black necktie. Personally I found that wearing a blazer and dark trousers was acceptable too. For ladies of course, dressing up is expected, but my wife gets away with wearing either white or black silk trousers and a fancy top.
On formal nights 99% of the men wear dinner suits, but if you do not mind looking the odd one out, then it is up to you. You must understand that the formal evenings are part of what makes the QE2 experience what it is.