I have to agree. I think the HD camera actually makes blue screen effects look far worse. I still disagree with the decision and believe film would have been more suitable. But I will say that the effects in the trailer still looked better than AOTC's.

As for Grievous, I have one theory one why he was introduced. Obviously I agree with the action figure and Vader origin arguments. Note: I have not seen any spoilers, so this might sounds stupid. Samuel L. Jackson made a comment somewhere that he asked GL prior to Ep III to make sure his character did something integral to the plot before being offed. Perhaps GL needed to appease SLJ by creating a powerful villain for him to beat.