I have played it - and really enjoyed it so far. The open world has a good size and the races are fun. There's even an element of replayability to them that I enjoy a lot. I don't know if that has ever been done before, but one (optional) winning condition is to collect K-A-T letters (THPS-style) and win the race. It's a nice breath of fresh air that even doubles as a way for the player to learn shortcuts.
I've not yet raced any of the bosses, so can't say how much fun those are. But the game itself is a charming little Indy game that I enjoy a lot. Also worth mentioning: The soundtrack is amazing and there seems to be a fair bit of restraint in terms of collecting stuff in the open world. No scouring the world for 6247 hidden whatever's.
Concerning the cars: the ones that drive around are all pretty small and have a charming retro aesthetic - I don't mind them. Especially since the game makes it very clear that bikes are the cultural cornerstone of the world. There's also not that many of them - just enough to make weaving around them fun without being overbearing.