If you are looking at the Biopace/Rotor/O-Symmetric relationship as similar due purely to aesthetics, or their similarity due to their lack of similarity to round chainrings then, yes, they are similar products.
But, that said, from the RotoR website "The Q-Rings are elliptical; the Biopace and O.SYMETRIC chainrings are asymmetrical.". And Sheldon Brown points out that Shimano called Biopace "point-symmetric egg curve". Which really only gives them the similarity of being different from the norm which in this case, is a round chainring, but if you go a step further, they are quite different.
So, to try and answer the question posed above.
- The first difference between RotoR and Biopace is elliptical vs. asymetrical.
- The second is the inherent purpose which, as previously stated, is that the Biopace chainrings placed the maximum tooth size at the dead spot while Q-Rings (RotoR) have the minimum tooth size at the dead spot. RotoR claims this is to increase your ability to get through the inefficient spot of your pedal stroke. Biopace is supposed to speed your way through the power portion (less teeth) and use 'stored' energy to power through the dead spot (more teeth)
- Which leads to the third difference which is the adjustable nature of Q-rings (RotoR). Since my dead spot could be different from your dead spot (and would ideally be analyzed with some sort of spin scan) you can adjust where the minimum tooth size sits in relation to the crank arm.
So, to simplify it (perhaps too much) RotoR claims that it is more efficient and better for your knees etc. to minimize the tooth size at the dead spot and maximize the tooth size where you generate the most power and are the most efficient.
Having installed a set and seen the power file from a MTB powertap I can vouch for the fact that it appears to 'smooth' the application of torque while mountain biking. The thought behind this is that by smoothing out your application of torque you will be able to ascend technical climbs ... better. That is one coaches take on the Q-rings and why he sees benefit.
So, that all said. Have a gander at Sheldon Browns take on the issue of Biopace. Essentially, to try and summarize his thoughts, Biopace is striving to achieve the exact things that RotoR is trying just by going about it in what appears to be the completely opposite way.
In fact, he even mentions the application of Biopace to mountain biking and how it evens out the application of power to the cranks.
IMO it is all very confusing. RotoR does trot out some scientific studies and I can attest to a difference in torque application on the mountain bike. In my experience, what is universal with RotoR and O-Symmetric is that the shifting is ABSOLUTELY terrible. Add mud to the mix (MTB) and it goes from terrible to non-existant so whatever perceived benefit there is ... I think you might lose with poor shifting performance.
What is helpful from Sheldon's take is that it seems Biopace failed more due to clumsy marketing and poor communication than it did from being a poor design.
Lastly, I don't think any of them are 'GOOD' or 'BAD'. They are different and might work very well in some applications and poorly in others (Ie. RotoR and mud). But the Biopace choice is pretty much a moot point because ... you can't buy them new anyways.