16 years of aero road bicycle development have made the S-series the benchmark aero road bike. These bicycles are not only faster in the wind tunnel, but proven in the real world, and stiff enough to win professional sprint finishes.
Strengths: This is for a 2014 Cervelo S3. I've been riding the new 2014 Felt AR, which is clearly a very fast bike, especially on the flats. What I don't like about the AR is how flexy the front end is. I especially feel that when I am sprinting and out of the saddle climbing. It just plays with my head. I have also owned a 2011 S3 and sold it for the same reasons as the AR. I can say that the new S3 took complete care of that. It is extremely solid. It sprints and climbs almost as well as my TCR Advanced SL and overall is a faster bike. If you are looking for a solid, stiff, comfortable aero bike, I highly recommend the S3. I will be racing it tonight.
Weaknesses: It seems a little heavy just as all aero bikes do. However, I have found that the added weight does not hurt me in Oklahoma. We have flats and rolling hills and short punchy climbs.