I've been lucky enough to put a few hundred miles on a demo set of these wheels and I've been nothing but pleased. To indentify where I'm coming from, the wheelset usually on my bike is a pair of Reynolds Assault clinchers, so my comparisons will largely be based on that frame of reference.
The Zipps feel stiff, and I am able to run my brake pads a few mm away from the braking surface without any contact between those parts under heavy sprinting loads. I weigh about 200 pounds (91 kg) and put out about 1300 watts for my five second power last time I rode with a power meter, so I tend to notice when wheels are flexy.
The braking on these wheels has been the biggest surprise; it's excellent for carbon. I've ridden these wheels in a wide variety of conditions, including a 10k descent in the rain, and not once did I feel a lack of confidence under braking. Additionally, there are no disconcerting sounds under heavy braking, which is sometimes the case with carbon clinchers.
The 302's come with J bend spokes, which in my experience work just fine and are easier to service/replace if necessary, and do not have the dimpled surface found on Zipp's top end offerings. I'm sure that in a wind tunnel this would be a measurable difference, but in the real world, I was completely content with the smooth rim surface.
I will say that the seam between between carbon sheets on the inner lip of the rim (the portion closest to the hub, where the spoke nipples are) could be a little bit cleaner, but bearing in mind the price of this wheelset relative to other carbon clinchers from trusted brands, it's not enough for me to knock a star off the review.
All things considered, this is one of my favorite wheelsets that we carry. For the sake of comparison, For $1,500 you get Zipp reliability, noticable aerodynamic improvements, and braking that you'll feel confident with on prolonged descents. Going up in price beyond $1,500 will yield a wheel with some more features and very similar performance; what it really comes down to is whether those relatively diminished returns are worth it to you.