Mammoth is a truly great mountain, big and with excellent snow conditions, a great variety of terrain - the only problem is that in can get crowded, especially on weekends and holidays. Luckily Mammoth is huge, has a million lifts, and can accomodate riders better than most resorts due to its excellent layout. It is not hard to escape the crowds if you stay away from the lodges and the big runs that feed into them. At 3:30 on a weekend afternoon, the main runs going to the lodges look insane, with riders and skiers all piling their way down the same run to the bottom - you might think you are in a Japanese train station, it is literally wall to wall skiers and boarders. If the top of the mountain gets socked in or too windy, it will be closed, but luckily there is still plenty of room and good riding to be found around the fringe of the resort, toward the bottom and sides of the hill which in and of itself is expansive. Mammoth has huge trees nicely spaced, with some great tree runs, even greater open bowls, with plenty of steep chutes and cornices to launch yourself off. If conditions aren't ideal, there are plenty of smooth fast groomers to enjoy, and more terrain parks for the adventurous "jibbers" that the reviews below complain about than just about any resort in the country. The many lifts and riders make secret corners and runs a little hard to come by, but they still do exist, and you can move from one end of the huge resort to the other in just a short sequence if you are thoughtful, (and if the top of the mountain is open).
Like it or not snowboarders are here to stay, and listening to luddite skiers whinge about the good ol' days gets tiresome. With Mammoth being the closest major resort to LA, and its huge population of surfers, there are sure to always be plenty of snowboarders around Mammoth, and Mammoth is probably snowboarding central in the USA. There are some pretty gnarly skiers plying their trade here as well too and I have seen them fly twenty or thirty yards off jump and drops at Mammoth as well. If you don't like snowboarders, go to Alta, Taos, or Deer Valley. If they are too far, try June Mountain down the road, which is much smaller and less crowded, but still a fun day or so for a change of pace.
Mammoth is about as good as it gets in just about every way.