Yes, the museum in Gatow is huge (by German standards
). The planes inside the hangars are all well preserved while the ones standing outside are in a poor condition.
BTW there are also many WWI replicas (some even flyable) in one of the hangars and there are also radar stations and SAMs on display.
It is definitely worth a visit especially since it is for free (although I would gladly pay 5€ and see the planes outside be restored to their former beauty...but I guess that is what the frequently ignored donation box is for).