A little odd... and it may be my laptop rather than the game so sorry if its the former!
I always install a new version in a new folder in Program Files, then copy across my saved games and key. But this latest version is super jittery (like its lagging) on the menu and then is ok when I start playing (EDIT: ah actually now its super jittery in gameplay as well!). The mouse moves really slowly and I have to click 3 or 4 times to time it so my click coincides with a gap in the jitteriness! I have tried switching to 'Fast' mode but it makes no difference and in any case, the older version runs fine!
If you have any info on this it would be greatly appreciated. I have kept the old version for now just in case it's my laptop!