Pros:

Unlike many "Balloon Race"-esque maps where there are two vehicles competing to reach the end of the map, Wacky Races actually manages to maintain class balance.

Scouts, Pyros, and Heavies shine at the areas where both cars come to a standstill and there is a lot of competition to push through. Spies can also be devastating here.

Soldiers, Demos, and Snipers hold a strong but not domineering presence in the map by setting traps, shooting inside the buses, and being able to function independently outside of the buses without much trouble.

Cons:

The map does have a few collision bugs with the vehicles, where you often get stuck inside of them while they are in motion.

It can also be painfully difficult to win the game once the opposing team has enough of a lead on you, as attempting to stop their van also means abandoning yours.

Conclusion:

Overall, this is a great map for having fun without worrying much about serious play.