We visited the Alcazar in Toledo on the first day it was open to the public after being closed for years. I think it was worth the waiit.
On a series of multiple floors, every era of Spain's military is chronicled, from the Roman period (they show you the cisterns under the Alcazar's foundations) to the present time. The exhibits are extensive and interesting. They are both static and multimedia. The captions are in both Spanish and English. I think, after that morning, that I have seen every piece of armor and every flintlock and every uniform in Spain's history...
Perhaps my only criticism of the museum is that, if anything, it is too comprehensive. But, that said, what's not to like? Just skip a little, if you like.
If you have interest in military history at all, and you're in Toledo, don't miss this. Even if you aren't interested in "military" history and you're just interested in Spain, don't miss it.