Island Cruises also offer informal cruising in the Med and Carribean. I have been on Ocean Village Two and Island Cruises 'Island Escape'. Thouroughly enjoyed both. In my opinion, the level of informality, friendliness and 'feel' is the same with both companies. Island Escape is an old ship, however, and not as nice to look at as Ocean Village Two so I'm trying the Island Star next year. Have a look at the Island Cruises website for more info.
Norwegain Cruise lines (NCL) offer freestyle as well.
I recommend the Island Star, just back had a great time, informal cruising, liked it so much I'm looking for a good deal for next year.
I to have cruised with island cruises both on the escape and the star . the star is a much nicer ship , but could not complain about anything on either of the ships. food good,entertainment excellent staff very friendly, had a fab time. could dress up or dress down if wanted.and on both ships the captains were great fun and had a good laugh with the guests.
Have sailed on OV and OV2 many times, but have never had any benefits as a returning passenger...Have just been on rci Independence of the Seas not strictly informal but certainly in no way intimidating and there was only one formal night which was lovely..try it..