Probably one of my biggest pet peeves with the series is that Obi-Wan feels spot on but Dooku is way off. Nowhere near the quality of Sir Lee, even given his limited screen time and role.
I thought Sir Christopher Lee did just fine. He did much better than most actors in the Prequels.
On a side note, I don't care too much for TCW's Count Dooku. I don't get the same vibe from him as Sir Christopher Lee. Not that anyone could actually replicate Sir Christopher Lee, but TCW Dooku doesn't feel like Dooku to me.