I always think the mark of a great game is when you get beaten by someone, and nod admiringly at their tactical prowess and what they've pulled off in terms manoeuvre, rather than roll your eyes at a ridiculous army list or ridiculous/nonsensical abstract playing of a rule.
Had it when I got thrashed comprehensively in a SAGA tournament by an Irish player (faction, not his nationality

), his bog-trotting forces using terrain to whittle down my lumbering Anglo-Saxon horde before closing in for the final coup d'grace, was something straight out of Sun Tzu. And a couple of times in Infinity as well, where an opponent has set up something to make a 'no-win' for me. Of course, better if you do can do that to them instead

(but, like you say it's definitely something if you can learn from these games!)