Honestly, I don't find the prequels quite as crappy as everyone else does(for one thing, I don't hate Hayden, just the scenes with him and Portman and his addition to ROTJ), but I think the biggest problem with the prequels have to do with the terrible, terrible job done with the editing. Revenge of the Sith for instance should have been a half hour longer and given some more depth to Anakin's fall.
Hayden as an actor is good, what failed completely was the character Lucas wrote, Anakin should have been a good guy who is forced at some point to turn against his beliefs in order to save his beloved wife (tragic, forbidden love). i know it's all in the movies except one little tiny detail, Anakin being a good guy... he is fighting for good guys indeed, but he certainly isn't that good, murdered at least 50 tuskens, murdered disarmed sith who wasn't much of a threat after loosing weapon and both hands, disobeying jedi order, whining about Obi's teachings, rebelling jedi order, questioning jedi order teachings, motives, actions etc. etc. ... where's that great pilot and a GOOD FRIEND Obi told Luke about ??? all I can see in Anakins charracter is that he behaves like a spoiled child in EP II and even more spoiled child + teenager who hates life in EP III
btw. what even caused the crisis in EP II beginning and how was it connected to ep I, asking because I find EP I completely useless in whole picture (story wise)
The only prequel movie which is at least good is EP3 the rest is a waste of really good material for a movie in my honest opinion... prequels should be rewritten from scratch and it should be JJ Abrams who do it