For months, the dust / oil stain problem of D600 was hushed, affected customers (I know of no-D600 user who was not affected) were put off with sensor cleaning and closure change that could not resolve the issue. Nikon Germany can not even because probably something for the very well-sought service followed only internal transfers from Japan. And now the D610 - what a bankruptcy! Nikon could also write: "Sorry, that is a bad design D600, we get the problem under control, version 6.10, however, is finally properly constructed" (the evidence is still pending). But how does this affect the customer? Prices for used D600er fall into a bottomless pit, while the street price of the D610 is back, where the price of D600 was at the beginning - this product has not improved, there is only a finite not defective. And listened to with 6 instead of 5.5 frames per second (no one remembers) or "improved white balance" (the white balance of the D600 was properly), this is old wine in new bottles, and the customer is the loser. Who a D600 now sold second-hand to buy a D610 with no dust problem puts several hundred euros on the table to have at the end, he was already should have received with the D600.
As for the picture quality of the D600 / D610, so everything has been said, but not yet by everyone. The sensor is mE probably the best FX sensor on the market, as regards the compromise of data size, resolution, dynamic range and high ISO. The camera is however incapacitated artificially small and for many power users by Nikon equipping them with the totally undersized and relatively slow DX AF module of D7000 (it has the D7100 module the D4!), For example, also lacks 100% - View at your fingertips and the better leathering of the Pro models. One D800 with the sensor and the frame rate of the D600 / D610 would have been too easy.
To review: The D610 gets good three and a half star, without the deliberate "bottlenecks" they would get five. Half a star deduction is available for the price of, by the "model change" now again 300 - is too high.
Edit: For dealing with customers of the D600 you should really again two stars pull off, but that would not do justice to the D610 itself.