Runaway conditions vs. equalizing effects. Taking either to the extreme leads to not very fun games. With strong runaway properties, if you're first to get an advantage, you quickly become untouchable and the game becomes a foregone conclusion. On the other hand, if the equalizing effects are too strong, nothing you do really matters because the playing field is continuously leveled.
So, having the correct blend will be a core element to any game.
In your opinion, where do you prefer games to be, and why?
What do find/think different audiences prefer? Casual/serious gamers, younger/older, mainstream/niche etc.