I've only taken a couple of hundred pictures with the D7100, and I am still very impressed with what comes out of it. I've shot at ISO 100 all the way up and had acceptably good results through 4000 or higher depending on overall conditions. I also shot these with everything from the kit 18-105 to 1.4 Primes, once again yielding great results. I purchased this as a travel camera with the 18-200 VRII and really like the fit.
As a side note I had the D7000 in the pass and the picture results with the D7100 are worth it. I also have a D700 and a D4, but I will love this camera for the daily run around taking pictures when I travel, for is so compact and light.
Nikon Camera's D4, D700, F100 - Nikon Lens 50 1.8, 24-70 2.8, 85 1.4D, 70-200 VR 2.8