Zombie Driver HD, is almost the same Zombie Driver game but the HD version has more missions and some vehicles + new skins for older vehicles. Except that is almost the same game. I said "same" since the keyboard keys still can't be changed, which is strange but well some might manage it while I didn't like it at all. I mostly use Z instead of S and well since I couldn't change the keys I was forced to get used to using S.
But, I never encountered any bugs during the campaign play which is quite ok with me since I wanted to play the whole campaign and see how the story evolves. I said story but it's a very simple story, a corporate experiment goes terribly wrong, the army can't interviene (no idea why) but I can :P. A simple taxi driver, who over the course of missions can get some nice weapons and some part upgrades and a lot of money :P
The campaign is simple, some missions, not really making any sense but well, at least playing the campaing went smoothly and I finished all the missions very fast. Some missions were interesting while others were both hard and boring. The only problem I had was during the missions with a vehicle without any weapons (a bulldozer and a truck). But I managed to finish every single mission very fast and thus complete the campaign which was decent to say at least. I think the game in co-op would be way more interesting if the 2nd player could either ressuply or repair the 1st player :P Maybe in Zombie Driver II?
I never tried the Blood Race or Slaughter modes so I have no ideas about them. I did enjoyed the game, some vehicles are amazing at killing zombies, some are slower but manuvrable while others move fast but are not that durable. Depends of taste, there's a lot of vehicles to choose, the ones introduced in an DLC are quite awesome and probably the best all-around to use.
If you like a "drive a car with weapons and kill zombies" game, if you can adapt to the "no keys remaping system" try it :P You might be suprised and the campaign will take some 4-6 hours to finish, depending of your playing style and well pacience :P