I went the Friday after Thanksgiving, and it was very crowded, but still fabulous! It's amazing what they can create with Legos!!
The children in our group were almost 7, 8 1/2, and just turned 11, and they all had a great time. We went on 2 of the 4 roller coasters (the dragon and the wooden one) and they were tame enough for the whole group to on, but still fun.
DS (the 11-year-old) said Mini-land was his favorite thing of all, though! Definitely allow some time to wonder around there.