My son had a partial knee replacement, and says there is no pain whatever now. But how limited he is, I couldn't say. He is not the athletic type, doing all sorts of sports.
I myself am looking at knee replacement as my next option. Right now I wear an "Unloader" brace. I hate it but I can walk with it. My surgeon keeps telling me I'm too young, too. I go to see him again in the fall.