We had a formal night but it felt like overall people dressed a lot less formal than our other Disney cruises. Maybe because we were already having to pack so much warm weather and hiking clothes?? I ended up not changing for dinner on a few of the nights and just wearing my jeans and a Disney shirt (as opposed to the dressier clothes that I had brought intending to wear to dinner). Maybe it was also that we got back on the ship later than a lot of the other ports I have been to? So we just rolled with it instead of spending time dressing up?
If you WANT to dress up, definitely do not let that deter you! There are still all the photo opps and fancy foods at dinner and all that. We did one fancy night just because it was our 25th anniversary and we wanted nice pictures. But if you want to be a little more casual and still feel comfortable at all of the dinner rotations, that's also fine and normal.