Couple points:
The special effects are impressive and revolutionary, but I'm not sure if I'd say they weren't a failure in filmmaking. George created some really cool worlds, but none of them seem lived-in. The characters never interact with the worlds they're in because the actors themselves have no idea what those worlds are like. It all ends up feeling artificial and kills my suspension of disbelief. In the case of action scenes, There is a lot happening on screen, but nothing of substance is going on. It's hard to follow and there is no stakes to the battles, especially considering it is all powerful Jedi vs robots. Special effects are great, but what's the point if you don't care about the movie?
Nothing wrong with exposition, but the prequels fail in two areas. The first is what Knick alluded to, telling and not showing. The obvious example is that we're told Obiwan and Anakin are friends, but they seem like bitter rivals from the beginning of Episode II. Obiwan already dislikes Anakin in the first movie. Would've been better if the series started with Anakin as a padawan, with the two of them at odds early on but eventually developing a close relationship. Something like Han and Luke from the original, except of course their relationship deteriorates by the final film. Or forget all that and just not have them split up into separate adventures in II and III, so you can build their relationship on screen.
The other problem with the exposition is that Lucas wasn't creative with the way exposition was delivered. It was always walking and talking or sitting and talking. Always in a sterile location. No sense of urgency, even during major plot points. The characters don't seem to care, why should we care?