My vintage Cannondale R400 from 1989 has a Shimano "Biopace" Chainring, which is oval.

Can't say I really notice the difference. I don't dislike it in any case. I woudln't spend extra money on it.

It was supposed to be better for the knees, but it never really took off. Some pro's even ride oval chainrings I think, so it might just be personal preference.