They are bad, but not that bad. Episode 3 is quite good outside of lame key scenes (which means that most of the movie actually works fine),
Which scenes aren’t lame and work fine?
Most of the opening, from the crawl to the “happy landing”. Most of Palpatine scenes before he reveals himself as Sidious (Opera scene is very good). Most of the Kashyyyk scenes (all except the Yoda leaving in a tiny spaceship thing). Obviously all of “order 66” (except Anakin killing kids). All of Mustafar duel except a few dialogues. Obi-Wan at Utapau going rogue against Grievous (except Grievous death). Etc. Great stuff, great music, beautiful aesthetics, still strong cgi (except a few shots and elements that didn’t age very well). No wonder fanedited versions of Episode 3 are very good movies. But Lucas fails with the turning to the dark side scene. He should have kept it off screen, with this wonderful sequence as the real turning point (https://www.youtube.com/watch?v=_hoXNXSpmng), not the later bullshit in Palpi’s office.