The odd game out

Did I mention #1 is The Opera Game?  I have struggled more with this puzzle
than any of your previous ones.

These haven't all been solved yet?

Apparently not.

number VII???

 Very good, Boymaster. Two puzzles left, plus the biggie - which game is the odd one out. One last (well, maybe not last) hint for the two remaining games. They were both judged "best games" for the Chess Informant issues they appeared in.

Okay, time to post the full boards for IX and XI:

IX:

XI:

omg the guys playing black in both games are geniuses!

Only one question remains now that all games were identified...

Which game doesn't belong?

Yes, which one is "different."

Hint: the odd game out is "different" on a very fundamental level, it is a very, very simple question really.

This hasn't been solved yet?

It's a 960 game? :)

 No, all games are classical chess games. However, you are correct to take the "big picture" approach, this sort of a helicopter view should lead you to the answer.

Portisch-Pinter perhaps, because there's not a world-champion (official or unofficial) involved?

 Good try, but Saemisch-Nimzowitsch falls into the same category. You are definitely approaching the problem correctly ...

Damn how'd I miss that? Well how about Morphy-Duke-Count because there's three players. That's got to be correct in one aspect :)

 This is an unexpected factor which I did not take into account. The Morphy-Allies is indeed unique... Can you still find the more obvious criterium I originally had in mind?

One more hint. You don't have to be a strong chessplayer to guess the main question. It is enough to know the basic rules. But the main question cannot be answered without knowing the basic info about all 16 games in the puzzle.

Hmm... Is game of the century / Byrne-Fischer, the only one where castling doesn't take place? I don't know all of them and am too tired at the moment to check. Just guessing, really.