Honestly, watching the prequels after having watched and rewatched so five seasons of The Clone Wars is a TAD hard for me. Don't get me wrong, I can still find plenty to enjoy, but overall I think the writing on that show surpasses anything done in EITHER movie trilogy.
More or less, I watch the prequels when I want to see badass live-action lightsaber duels. Every one of them is chock full of them, but only one of them has two of the hands-down coolest characters in the saga; Qui-Gon Jinn and Darth Maul.
That's what YouTube is for. Any time I really feel the urge to watch the prequels, I just pop over to Youtube and queue up all of the lightsaber fights in individual tabs, let them buffer, then watch them all in one go. No need to fast forward, or otherwise suffer through having to watch Jar-Jar or Hayden.
As for the quality of the actors...well, Mark Hamill was kind of whiny in A New Hope and even in Empire, but he managed to be whiny in a way that isn't incredibly irritating for the audience. It's clear, however, than most people could have done without some of his character in those films, as if you watch most of the major spoofs of Star Wars, they either remove Luke entirely (replacing him with basically a Jedi Han Solo), or overemphasize his behavior. That isn't to say that I don't like Luke, or the original trilogy, just that I feel like people neglect some of that.
All of that said, Hayden was abysmal, Portman was terrible (and she can be an really good actress--see Black Swan, for example), and I found Ewan McGregor's Obi Wan to be in turns either too stiff, or oddly reckless...inconsistently so. Honestly, I think the best performances in the prequel trilogy were turned in by Yoda and Ian McDiarmind (Palpatine). The director wasn't the only one who failed the actors and viewers alike--the writing was similarly awful, and not just the script, but also the whole plot. Really a shame.
The best things to come out of the new trilogy were Due of the Fates, and the lightsaber duels, and I suppose a revitalization of the IP, although we could have done without all of the retroactive edits to the original trilogy.