I actually handled a 1926 Nagant today at a gun shop in New Hampshire. Nice, different, I'm just not sure I get it. Even the shop owner couldn't understand why they had been developed.
I did get sort of a history lesson. He said the Russians contracted with Smith and Wesson for 30,000 of their top break revolvers in the late 1800's and then Nagant decided to develop his revolver and Russia adopted it. He claims that loss of business almost put S&W out of business and they sold their patents for the top break russian design to Colt. I'd love to have one of those right now. That is a gorgeous looking pistol!
My understanding is that Nagant designed the revolver (I think he may have filched the concept from Pieper, but I'm not sure on that) and tried to sell it to various European countries, but the Russians were the only ones to show interest--they were looking for something to replace the S&W that was a bit more modern, the "gas seal" design hooked 'em I guess...