Every MMO have their ghost levels. That vaccum place where you can't group with totally new people, and neither can group with everyone at the level cap. Basically, is a place where you have to learn to be self-sufficient and solo most of your XP. For most MMOs, this is all the game besides the level cap. In DDO, because of the TR mechanic, we have a good influx of veteran players always leveling and willing to group with others.
This do not mean DDO is free of the ghost levels. At the moment, it sit at level 11-16.
At level 11, veteran TRs take off a big bunch of their shiny toys from the TR bank (Shroud equipment, Minos, RR +6 stats, RR 30% striders, RR Greater false life ring, etc), and most start to solo, since the quests start to be more brutal, and dragging an unknowledgeable (yes, this is a word now) person around bring... issues.
At the same time, this is the time where self-healing become an issue for first lifers that do not play a self-healing caster. Potions start to heal less and less, you start to get equipment that rocket your HP bar up, and the monsters start to deal a lot of damage because they know some classes get a bump on self-healing by now (Radiant Servant II, Heal, Death Aura, Reconstruct).
So, new players usually hit a wall on grouping by level 11, and it get worse all the way up to level 16. At 17 you can group with capped people without an XP penalty, and the problem lessen a bit.
With the new level cap, I believe this vacuum zone will turn out to be the levels 11-21. There is a problem that one of the NEW levels will already born as a ghost level.
I suggest 2 small changes to lessen the problem with those levels:
-Heroic content will cap everyone to 20. So, if you are running an heroic quest/raid (like Shroud or Amrath), you will be trated as being level 20 for XP calculations.
-Epic Content will have no power leveling penalty. You can run at level 20 with level 25 people and not receive 0 XP because of it.
I know some people would vote for the XP to those levels could be twinked (both at XP requirements and quest XP) a bit to be shorter and faster on second and third lifes. The problem is, in the long term, this would just turn the ghost town effect worse.