Someone named borgmatrix summarized the problem of time wasted in the prequels quite nicely:
Lucas could have done better service to the material if he would have found a way to increase the Anakin/Obi-wan screentime.
Look at ROTS. There's a lot of stuff he had cut/dropped in order to give the needed to time to Anakin and his fall. He could have lessened the time devoted to Anakin's fall in order to incorporate more Padme scenes, or to develop the Rebellion subplot, or get Boba Fett in there, or whatever. But he didn't, and ROTS was about as good as it could have been given the time contraints. He gave focus to what mattered most.
Now, if only he would have done that with the TPM and AOTC. Lucas himself has admitted that about 60% of the prequel story he had envisioned was in ROTS and only about 20% each over TPM and AOTC. By his own account TPM and AOTC are each about 80% filler. Because of that, ROTS was harder for him than he'd initially thought. He had less time to fit in everything he would have wanted. If he would have approached TPM and AOTC with more urgency and tried to make the best use of the time and space he had to tell the prequel story, these movies would have been better for it, including ROTS.
By doing more with the Anakin/Obi-wan relationship over TPM and AOTC, he would have saved himself the need to play catch-up in ROTS and given himself (and the movie) more breathing room. All three movies would have been more balanced and complete if he'd spread the plot out more evenly between them.
