Salt Factory is probably my favourite of this pack, it feels good to race on and it's a fun location idea. The rest is a bit of a mixed bag - Windy Hilltop is pretty deadly, but fun when you get used to it. No issues with Tux Raceway, but for the most part I find most the other maps fairly cramped. Frozen Lake and UAC in particular, I never really find a good flow to them.
As someone who's played a lot of source games, I appreciate the visuals Crash Course is going for :P