I don't think they are terrible, I think they are very flawed. They are a different style of movie than the OT for sure, and the OT is far more consistent. The PT would have been much higher regarded had they not been star wars films I think.

They are good films, they just aren't nearly the perfection of the original trilogy. And sure, hayden christensen's performance was terrible, but let's not pretend Mark Hammil was all that fantastic in A New Hope either. He was much better than hayden for sure, but he didn't get REALLY good until Empire strikes back. Don't get me wrong I strongly enjoy his performance in ANH, it's just not as perfect as it is in ESB.

Also, Ewan is very good as obi wan in the prequels I think, something alot of people fail to mention. (or realize). Whether or not you like the prequels, Ewan was a good obi wan. And he could have been better yes, but alot of that goes along with not having anything to react to, other than a green screen and somebody yelling "BANG".