The Grande Bretagne is fabulous and I highly recommend this hotel. If you had more than two days I would recommend going to Sintra by train. Add this to future trips to Athens.
We really enjoy Beefbar, it did require some experimenting with the menu items to fine what we liked best, but it is a positive for Crystal. We also preferred the lunch menu.
We say that “every cruise has its on personality”. We like long cruises and they always consist of different segments with different “personalities.” Sometimes it is good sometimes not!
We just left the Serenity after 40 days and loved the Beefbar for both lunch and dinner. We did not try all of the items on the menu but we did have many of them. We did not like them all, no surprise, but overall we considered this new dining option a winner.
You will love the new Beefbar restaurant. It fits your description perfectly. You can dine very casually with several light options or you can have a more inclusive meal with the all the options.