I always felt that the duel in ROTS could have been better if Lucas would have developed the friendship of ObiWan and Anakin over all 3 prequel movies. We got glimpses of their friendship in AOTC, and more so in ROTS, but not as much as was developed in the OT of Han and Luke. You had a real sense that they would do anything for each other. In the PT, it just seemed forced at times, but we already knew of their friendship going in, so it was easier to see whether it was done well or not.

My whole point is, can you imagine Luke and Han going at it at the end of ROTJ if Luke turned to the darkside. Putting aside that Luke would woop his butt because he was jedi, you would almost feel a real betrayal between them because they were great friends. For Anakin and ObiWan, it was just accepted of their friendship, and I think that hurt the duel because it should have been more tragic.