I'm having the same worry, but mirrored.
While I like having a flat EQ, I don't want it to be completely analytical. I also don't want the D400's to be bass-monsters with no other strengths, considering they're advertising them as having amazing bass, not advertising much else.
Sounds good to me... Flat bass down to 5hz, no recessed midrange and no treble spike at 7-10khz = win
The D2000 were too fatiguing and also the midrange was too distant