My first mountain bike and bike that I bought with my own money was a 1990 Giant Sedona that was shod with Biopace chainrings. I replaced them within a year for round rings. The pedaling was just weird. Fast forward to 2009-ish and I took a gamble on oval Rotor rings on my Salsa. Way better and smoother power delivery. Shimano could have developed Biopace a little more. I now have two other bikes with oval chainrings - Wolftooth and Absolute Black and they're both great.