At the high-level game, players have access to all kinds of powers that can change the game. This was always by design, from the early days prior to even the first edition D&D rules. Does one door lead to certain death? Okay, well, the players should have all kinds of divination spells to learn what is behind each door. They can cast disintegrate spells on the doors (or the walls next to them) to bypass whatever might be on the doors themselves. They can teleport to where they want to go, bypassing the doors altogether. They could animate an object or summon an extra-dimensional being to do the job for them. Or they could try far more mundane tricks to figure things out. Simply tracking footprints to learn which door has almost all of the traffic could solve the problem. That's exactly how my players operated - with a combination of character abilities and their own personal problem-solving (and trying to see patterns everywhere to give them further clues). I think that's how the high-level game in RPGs should go, in general. At high level, characters should be able to change the rules of the game, to make the unfair reasonable.
#4 - An open-ended approach to creating challenges, including a willingness to make them completely unfair against a "brute force" approach, and a willingness to let the player ‘cheat' his way to victory. And no more making ‘boss monsters' impervious to the most debilitating spells!