Higher than 10th level is just too much of a headache IMO. When I play, I tend towards spellcasters, and to really do justice with those classes, you've got to buff your teammates and keep track of those buffs. Haste, Fly, Shield of Faith, Magic Vestment, Bull's Strength, there's a lot to lay down and a lot to remember. If you've got a specific enemy lined up (such as a dragon or powerful undead), it can take an hour (real time) or so to do the proper prep before going off to fight.
And that's just from the player side of the table. On the DM side, it's even more of a pain.
IMO, it's all downhill after 10th level. I don't mind playing games of those level, but I vastly prefer the low-level stuff.