Actually there are quite alike. Particularly in the case of the NP22 and P226 for size. It is to be noted that the NP22 is based on the original P226 however. The P226 has since gone through some changes in the way the springs work, along with grip changes..
Action wise, the single action of the trigger of the NP22 doesn't seem as crisp and light(for a combat trigger) as the Sig, but the one I fooled around with was brand new. Double action isn't so hot, but then again, it works.
Can't personally say about durability(though Redleg from TSE has noted that it wears out quite fast, unlike some Norinco products that are built to last out a nuclear attack from the cold war and continue working). Apparently the frame rails get pretty eaten regardless of lube.
For the price, I would say from handling it(not owning and long term use) and others' experiences, it probably isn't a bad deal for the $350 or so. Personally, for the same money, I'll go for a Norinco 1911 and tinker with it as a project. Or for slightly more, a Ruger pistol for a tank of a combat pistol(kind of interested myself in a 345 or a 94). For a significant price more but still in the lower priced gun category, that Zastava Sig(just under $600) copy seems interesting if you want a SIG-like pistol. In that range you then open up yourself to the eastern block hehe(eastern european brands) because you have CZs, Grand Powers, ...