They deserve a lot of credit for Adam Johnson, he's improved so much since he's moved from Boro. He wouldn't be playing for England if it wasn't for City, so it's probably fair to say they have "produced" an England international.
Barry has stayed pretty much at the same level, and it's too early to judge Milner. Hart has improved but that was mainly down to Birmingham, and Lescott has gone backwards.
Par score imo, in terms of development anyway. But a successful top 4 team, which is inevitable for them, playing lots of English players is a good thing for the national team.