Dropping the "woo" from 100% on a crit to 33% (best guess) sucks.
The Nightmare Bastard sword went from being the best trash-killer in the game to a trash weapon no longer worthy of the inventory slots or the feat required to use it.
Heavy-blades as a TWFing Kensai went from viable option to a bad idea. Nightmare for Trash and Drow Khopesh for Red-names was a reasonable compromise. Now? It's Balizarde or Mornh . . . singl-head heavy-blades are dreck.
The Nightmare, and other weapons of it's type, were an equalizer for low-DPS toons (Bards, melee divines, paladins, etc . . .). Low-DPS toons could still contribute against trash making them able to better justify a party slot.
And best off . . . Nightmares would Hjeal Meh!
Seriously . . . revert this back to the pre U20 state. Compared to a lot of garbage in DDO that is considered acceptable I have to say in hindsight the Nightmares were not over-powered.
Make it so.