I always enjoy the first playthrough(s) the most, because learning the system and strategies is the fun part. Once everyone knows all the rules and how to beat me, it's only going through the motions as a social experience.
To me that’s a hallmark of a game that isn’t very interesting! If you can discover a dominant strategy in a handful of plays, the game probably isn’t worth your time IMO.
It's interesting that you said "how to beat me." You also get better as you play the game more, right? So it could be you learning how to beat them ;-)