While I enjoyed the prequels I have to admit the actors playing Anikin were lacking, I honestly think its mostly Lucus' fault as a director, he couldn't coax the performances he needed from them. The same problem shows up in episode IV with Hammel's performance, there a a few scenes where a better director would brought out a better performance,
Also Lucas clearly changed, got older, and made more kid friendly/marketing movies. Hell he changed from Empire to Jedi, ewoks shuld have been taller and better armed, but the lure of kid friendly, mr,eti g bonanza got him.
I sort of wish that George had farmed out the directing chores to other, imagine Ep 1 by Speilberg, Ep2 by Kasidin or Coppolla, and Ep 3 by Nolan.