@roboccs: I played all the NES games at some point, but I only owned 4-7, so those were the only ones I ever finished, I think. The ending of 2 was really familiar, so either I finished it during a rental at some point or I've seen a video of it.
I've never played 8 or 10, but I loved 9. It was one of those games I decided to go through in a bubble, so I didn't read any strategies or anything. I had a sticky note with each boss's weakness as I learned them so that I could destroy them in the boss rush at the end.
I never heard anything great about 10, so I never bought it. Maybe I will at some point. I wouldn't even know how to get ahold of 8, though that wasn't an NES game, so it doesn't really count to me.