I thought the Obi-Wan/Anakin friendship was completely squandered from the beginning. In TPM, Obi-Wan seems dead set against Anakin getting trained. That hardly sounds like "I was amazed at how strong the Force was with him. I took it upon myself to train him as a Jedi" from ROTJ.
That friendship should be the a central point in the PT because the fight at the end of EP3 would have been far more emotional and effective if we really felt that two friends were battling it out to the death. Instead, we sort of don't really care cuz these two never exactly seemed like good friends. The only thing that fight has going for it is that it's been lingering in our minds for 20 years giving it some sort of legendary status.
This is just one more thing in a long list of stuff that LucASS dropped the ball on.