So I worked on (at the time) the largest passenger ship in the world. It was Royal Caribbean Oasis of the Seas.
To respond to some points.
We had a smoking side of the ship, so smoking balconies, smoking areas etc were all confined to one side. Anyone caught smoking on the non-smoking side would be warned or disembarked.
Formal nights were optional. If you were dining in the main dining room, you were expected to dress up (many men in tuxedos and women in everything from cocktail dresses to gowns), but if you didn't want to take part, you could eat in the buffet in your normal clobber.
Speciality restaurants were always more formal dress.
There are places to go to escape the masses such as the library or some of the quieter bars. Some areas of the ship were less busy because nothing happens there. Ideal.
Other areas such as main promenade, activity deck etc are rammed most of the time.
Different ships can run the same area but with different itinerary, so if you want plenty of port time, you can see this in advance.
There are some brilliant, less showy entertainment options such as lectures (trunk shoe jewellers talking about creating jewellery/sourcing gems, watch specialist talking about history of watch making etc, guest lecturers talking about travel, history etc), activities such as wine tasting, backstage tours of staging areas, cooking classes etc. obviously you also have the OTT entertainment such as the themed nights on the prom, open deck parties, quiz shows, flash mobs etc.
Drinks packages are very expensive and the ship will sell you more duty free stuff than you're allowed to bring back to the UK which catches a lot of people out.
As staff, we were onboard for 6-8 months at a time. We sat through every 70s Night and heard every joke (and every idiotic comment). We smiled through being shouted at for the weather and for the prices. Racism from guests is awful.
The whole thing was big, brash, OTT, exhausting, so bright and colourful...crew areas were way more real and relaxed. Loved the experience, but like i say, if never go on as a guest.