We had a scheduled BA flight back into Heathrow. We just said which day we wanted to fly back and they arranged it. We live near Guildford so got a train to Southampton and were picked up unexpectedly by our Daughters on our return, we were going to use the train/bus/taxi combination to get home.
There is a lot of general info on the Cruise Critic Website Forum:
http://boards.cruisecritic.co.uk/forumdisplay.php?f=54As far as things to do are concerned it rather depends on the schedule of entertainment and activities for your particular crossing, you may enjoy some and not others. There are two show lounges, one of which has the famous planetarium. There are shows and films on every day of course. I seem to remember that there are opportunities to go behind the scenes, the kitchens for example, but I don't recall an opportunity to see the machinery spaces which tend to be off limits these days for security reasons. There is a viewing window at the rear of the bridge which was open most of the time on our crossing. We spent quite a bit of time in the forward bar/lounge overlooking the bows with a book etc. and the nearby library is well stocked with a lot of maritime related material. If the weather is good then the pool areas at the stern are pleasant places to spend time. There are gym facilities and an expensive spa if that takes your fancy!
Obviously, being Cunard, dressing up is part of the 'experience' and expected in the evenings. There will probably be two formal nights with the others being grades of 'smart casual'. I don't like dressing up myself but put up with it as I have always wanted to do a 'Transatlantic'.
You do of course have lots of opportunities to eat.... And drink.... And dance as well (I don't).
Most fellow passengers were pleasant enough on our trip but many will be Americans. As on all cruise ships you will see a smattering of 'plonkers' who are overfull of their own importance but QM2 has more space per passenger than most cruise ships so you are not forced to endure them. Basically it is a relaxing experience and the time does go quite quickly. On our crossing we had several different types of weather starting with an Atlantic swell and progressing through wind, fairly calm and finally fog!
I would recommend getting hold of a copy of the Haynes Workshop Manual on QM2
https://www.amazon.co.uk/RMS-Queen-Mary-Manual-Construction/dp/0857332449 but you might be able to pick it up cheaper or secondhand. It is written by Stephen Payne who designed the ship and is a fascinating technical read. I wish I had had it aboard with me as it would have been an invaluable reference to the ship and its workings. As it was I only bought it afterwards and realised how much I had missed!
Colin