Mammoth is awesome. The mountain is so deep that all the runs are fairly long, and it's really long coming down from the top (gondola) all the way to the bottom. It has some of the best bowls I've ever skied on up top-it's killer when it's fresh powder.
It can get crowdy on weekends and holidays but if you catch some fresh snow on weekdays it's spectacular. (The stormy weather can be fun too) But I've been to places in Colorado, Utah and East Coast where it gets much much more crowded- at least Mammoth is so big that the runs don't get too crowded except for the beginner runs. Perhaps the only other problem is it's little far to get to...Highly recommended!!