I am a very frequent cruises, having been on more than 50 cruises so I am a little jaded. When I travel with younger ones Royal is my top choice, so I have been on their sister line Celebrity about 6 times including this cruise. I had been on two Millenium ships previously, including one within the past year so I can comment on the refurb.
I really would give this 3 1/2 stars, not 4, but I didn't want to do 3, so 4 it was.
We paid for an upgrade and ended up with a Royal Suite which was very nice. It included free unlimited laundry and free specialty dining which was very nice.