Which cruise line matters enormously. Some are like Butlins and some are like the Ritz. Sometimes the passengers are 100% Brits, sometimes 70% Americans, and some lines are aimed almost entirely at Germans or French people. (The TUI brand aimed at Germans names its ships "Mein Schiff 1", "Mein Schiff 2", etc, just in case you were about to get on it accidentally.)
That said, if you are the kind of traveller who doesn't want to interact much with other people or overhear their conversations (DP's ears twitch a lot when other Brits are around, and I would not have a good time on a cruise where they assign you a table if I was sitting next to the kind of British man who calls his friends "squire" or makes borderline racist comments) then we found Aida to be pretty good. Not too expensive, informal, good food, almost everyone is German (but the crew are all Filipino/Indian/Indonesian and all speak English), nobody complains, and they have proper saunas (ooh, we do like a good sauna).
If you are a family then also look at MSC, which is a Swiss/Italian line. Not the poshest, passengers from all over Europe (so the shows are a bit "multilingual"), lots of stuff for kids, really good pizza available something like 20 hours a day.
Most lines don't include drinks (other than water with meals), so you have to decide what "package" to take. In our experience these are only worth getting if you either really knock back the booze (or the speciality coffees if you take the non-alcoholic package), or if you get a good price to bundle the package in when booking. If you buy it when you get on board you can pay $45 per day for the basic alcohol package, and the drinks a la carte, while not cheap, aren't usually extortionate either.