It's just a matter of perspective:
Viewed from a "historically blind" perspective, they are great cards. The fastest GPU around, decent power consumption - what's not to like? If the reviews are taking this perspective then they are absolutely correct. After all, they can't judge the cards against people's expectations, or against the speculated performance of yet-unreleased hardware.
Taking into account the norms of GPU technology though, they haven't lived up to the expectations that many people had of them. The drop from 40nm to 28nm is (proportionally) the biggest we've seen in a long time, but that hasn't translated into performance the way that it has with previous die shrinks.
One thing has struck me though:
The 28nm process allows (in principle) a relative increase in transistor density of 2.05 times (i.e. +105%), whereas the actual transistor density has increased by 'only' 74%. This is quite out of character from previous generations, which have more closely followed the expected transistor packing density (you can check the numbers on the wikipedia pages).
It will be interesting to see how Kepler fares in this regard. It could be that the more intricate design of GCN requires a somewhat looser transistor arrangement than the VLIW cores. But, if nvidia are also producing a ~70-80% increase in transistor density then it's more likely indicative of issues with the 28nm process. That's not necessarily to say it's down to issues with the manufacturing process at TSMC - it could be more physical problems associated with running high-speed transistors at such small sizes. If this IS the case, then we might not see such large gains from Kepler either.