For Prometheus, I was disappointed within the first 10 minutes or so and then it went rapidly down hill
I've not watch Clone Wars, but since George's input on them was limited and they are an entirely different kettle of Ewoks to the live action films, I may give them a go.
What I did find interesting watching the prequels was they way that the production team eased in to the CGI. In Phantom Menace they seemed unsure of how far they could push it. In the Attack of the Clones they seemed to be totally intoxicated with their new technology and just threw everything at it. Finally, in Revenge of the Sith, they seemed to have realised the special effects are supposed to advance the story rather than overwhelm it. Its a shame the central romantic tragedy featured two young actors with the on screen Chemistry of xenon and lead.