For the money and time involved in these movies, they're some of the worst ever made. Shoddy writing, wooden acting, and most scenes are laughably short. There are a few good fight scenes. Obi Wan v. Jango Fett (lol @ that name). Obi Wan and Qui Gon v. Darth Maul. Yoda v. Palpatine. Yeah, that's about it. I cringed at Yoda fighting with a lightsaber.
Lack of Han Solo hurts them too. There is no character or performance that resembles him. We didn't need a Han clone, but someone who was ethically grey, yet really is overall a good guy/hero was sorely needed in these films. Not sure why Lucas didn't use this classic motif.
What hurts the movies the most is the romance just doesn't work and just isn't believable. Portman and Christiansen have zero chemistry and it's a struggle to watch them together.
The good parts..
1: Darth Maul & Duel of the Fates
2: Windu and the arena fight
3: anything non-Padme
I think Revenge of the Sith is genuinely a good film despite the bad acting. Phantom Menace has too much gungans and droids, making it pretty horrible in parts and Attack of the Clones is the worst of the lot.
The writing in the prequels is just too horrible for me to stomach. Even in the comparatively okay Revenge of the Sith, you've got gold like: "Palpatine is evil!" "From my point of view, the Jedi are evil!"
Even Duel of the Fates isn't that great once you realise that John Williams nicked it from Dvořák's New World Symphony.