I've only been on one cruise and had a great time. I was seated with the same people every night for dinner. There was an additional charge for alcohol but a number of my dinner mates had brought bottles of their favorite beverage on board and had their cocktail in their cabin before joining us for dinner. The last night of the cruise one of them brought a bottle of wine to the table (also brought on board) to share a final glass of wine with all of us. I don't know if some cruise lines forbid that - kind of like not bringing your own snacks to the movie.
There was plenty to do on board at night with movies and broadway sketches and those were all free. This was an Alaskan cruise, so we were mostly sailing at night and staying in port all day. The days were long and it was never really dark but you have to sleep sometime.
There were plenty of excursions that were included in the price of the cruise and I took some of those as well as some 'extras' and was pleased with both.
As far as dressing up, there wasn't all that much of that. The men wore suits and ties in the dining room but a nice dress or pant suit is fine for the ladies. And, as someone mentioned, there are alternatives to sitting in the main dining room where the 'dress code' is less restrictive.