There are plenty reviews about Cunard's Queen Mary 2 (QM2) so this review is only to add a few points for 'new cruisers'. This is a beautiful, stately ship that's not for the hyper active family but has plenty to keep most people occupied especially the more cerebral.
I booked one of the cheapest cabins and the only regret was that with a window you could gauge what time of day it was but the money I saved paid for extras on board/ shore. The cabin was good, sailing very smooth (didn't know you were actually moving sometimes), staff excellent, food very good, drinks about same price as British pub prices except wine/ champagne which were more, spa treatments way too expensive.
I worried about being 'smart enough' and having enough evening wear for formal nights. Having been in the WRAF we had to wear full length ball gowns on such occasions so that's what I expected- don't worry, you can dress up as much as you want or not at all. People dressed down in the alternative restaurants and some ladies wore trousers or cocktail dresses on formal nights in the Britannia Restaurant.
Good size, plenty of space for clothes and people, very little noise and movement where we were. Clean and very well serviced, could do with a clock in room. Air conditioning seemed to blow directly onto me so had to leave locker door open above bed to deflect it.