The GTX 470 seems pretty good, while GTX 480 is good too. Neither are truly exceptional with respect to performance. Certainly not worth the upgrade for anyone with a high end DX11 card from ATI/AMD, as they would be better off by adding a second card. That said, for anyone new to the DX11 market, and/or for anyone coming from a G80-based or GT200-based card looking to play DX11 games and PhysX games, then GTX470/480 would be a worthwhile upgrade.
GTX 470 seems to be the better buy to me, and I think some reviewers got this completely wrong based on a very small sample size of games tested (hint: [H]OCP). GTX 480 costs ~40% more money, for only ~25% more performance than GTX 470, with the exact same feature set. And there is no doubt that GTX 470 SLI will have far higher framerate than GTX 480. Power consumption is reasonable too on the 470. According to PCPer review, idle power consumption on GTX 470 is only ~ 6% more than HD 5870 (load power consumption is ~25% more than HD 5870, but still within reason). Looking at a wide variety of games, it seems that performance of GTX 470 is closer to HD 5870 than it is to HD 5850, and in many games the 470 is as fast or faster than 5870.
In the Anandtech review, the author mentioned that there is a problem with the new Transparency Supersampling (TrSS) mode being too aggressive with supersampling, which causes the framerates to tank when enabling this setting on GTX 470/480. So that would explain some of the oddly low framerates in two of the four games tested by [H]OCP. Apparently this issue will be fixed with new drivers, release 256.xx.
One area where GTX 470/480 really seem to excel is in keeping a relatively high minimum framerate at graphically intensive settings, so real world gaming performance should be quite good. And of course these cards are relatively strong with extreme tesselation settings.
There is no doubt that GTX 480 is louder than most of the other cards in the test suite, but I think that some claims of 70dB are highly exagerrated due to having the sound level meter placed very close to the graphics card. Hilbert @ Guru3D measured 37dBA at idle and 45dBA at load with the sound level meter about 2.5 feet away. Keep in mind that sound pressure level increases by 6db for each halving in distance between sound level meter and source. So Hilbert's 45dBA at 30 inches away would result in 69dBA at 1.875" away from the card. Pretty big difference in sound pressure level there. And of course having 30 inches of space between ear and PC seems far more realistic than having only 2"!
Looks like GTX 470 and GTX 480 are about 15-20% short on performance to really catch people's attention. These cards give NVIDIA a competitive product in the $300-$500 price range, but certainly not a dominant product by any means.