The only 10/10 game I can think of is the first Half Life. I'm seriously struggling to think of others. Even CS, take any version, I don't think I could give a 10/10, and I played that freaking game for over 10 years. EDIT: Maybe Warcraft2/Starcraft 1?
I don't think I could give any game more than a 9.5/10 or 9.8/10. Maybe Unreal Tournament or Unreal Tournament 2004, Quake perhaps. It's hard to say. I can usually nitpick about one or two things that could have been done better in most games. The games I mentioned are probably the hardest I can think of to pick apart. And that's basically going back to how I viewed them when they came out and not by today's standards.