We were on the Millennium in August in the Mediterranean...
Nothing resembling a "chocolate buffet"...but desserts in general were excellent...They did do a sorbet thing out on the pool deck during at sea days...And there was always very good FREE ice cream in the buffet...
As to night time activities, they have all the typical stuff...a main show, karaoke, casino, dancing, movies, piano bar, disco..........................Never had a problem finding enough to do at night...