Yeah, it's definitely a case of Lucas' reach far exceeding his grasp. In the hands of a better writer, it could have -- should have -- been really compelling.
And the prequels aren't bereft of good stuff:
- A lot of the Jedi characters are cool, even if the Jedi Council as a whole is a mess.
- The art deco style of the late Republic is awesome.
- Natalie Portman is great.
- So is Ewan McGregor.
- General Grevious is interesting.
- Palpatine's plan of creating a insurgency for the Republic to overreact against isn't terrible (although it's the kind of thing that sounds good in fiction but tends to be a hapless failure in real life).
One can make a similar list for the sequel trilogy. But in both cases, they needed a firmer (and better, sorry, George) hand at the wheel.