I think that the context and setting for the prequel movies is amazing: Galaxy at war, Trade Federation/Separatists vs the Republic, a look into the politics and corruption of the day in the Senate/Jedi-Council. It has best backdrop of any Star Wars trilogy.
My issues is just in the execution. There are numerous times I'm literally cringing or laughing at the dialogue/acting (in parts where you are not supposed to be).
Revenge of Sith is a great movie in my opinion, but it is Episodes 1 and 2 that struggle a lot when re-watched with a modern eye.