I watched ROTS tonight and I have to say I enjoyed Grievous more on this viewing, the first time around he just seemed a foil for the tech that would be used to save Anakin.
His initial scene where he coughs and splutters and his two henchdroids do the fighting is ok, but it's his battle and chase and battle (in that order lol) with Obi Wan that is when he's at his best, and I love the fact Obi Wan stops him just before he gets to his ship and then uses said ship to escape. The line about the blaster after he shoots him is great as well.
On a side note I couldn't help but laugh when The Emperor finds what is left of Anakin and proclaims "He's alive!" as he lay there with no legs, half an arm, no flesh and two eyes. I half expected Palps to shout down to him "It's just a flesh wound, some sticking plasters and savlon and we'll have you fixed in a jiffy!"