Six Flags Magic Mountain is no where near as good as Universal, Busch Gardens, Disney, etc. as far as a theme park is concerned. Organisation and staff there just don't even come close to what the other parks have to offer, and just doesn't have the same 'feel' as the others. Having said that, the rides are excellent
We went last June, and rode just about every coaster in the park, and loved every minute of it
Queues can get a bit long as the ride attendants don't seem to have a clue what they are doing half the time, and end up sending cars around half empty rather than filling rows up with single riders etc. Which is another tip, be on the look out for single rider lines. Several coasters have them, like Deja Vu, but they are very easy to miss, so keep an eye out if you don't need to ride sat together.
Go to Six Flags expecting some great rides (if you like Coasters, its got very little else), but don't go expecting a great theme park, because it just doesn't even come close to Busch, Universal and Disney. Also, if your going during June the place seems to get swamped by school trips, which makes line cutting inevitable, and the staff really don't seem to care one bit [:(]