The first fight between Obi-Wan and Grievous is a mess, in my opinion. It seems they didn't really know what they wanted to make of the fight or maybe it was changed because they didn't have enough time, but it's quite sloppy.

The compositing job done on McGregor is quite bad. They even used footage of McGregor that was shot (but cut) from the Mustafar duel with Anakin and it shows. The eyeline between him and Grievous are way off too. None of the elements in the scene really match.

Also, the whole background doesn't make any sense. When Obi-Wan looks down on the Separatist meeting, Grievous we see that the floor is flat. But when Grievous pushes Obi-Wan back, they are walking on beams. And where is did that thing Obi-Wan dropped on Grievous' guards, and their bodies, go?

Personally, I'd rather see the scene go and have the confrontation between Grievous and Obi-Wan be interrupted by the arrival of the Clones even before they fight. If you want to show how badass Grievous is, put in the deleted scene of him killing Shaak Ti aboard the Invisible Hand. Much better, if you ask me.