Pros: Clean engaging bass, very comfortable (for me)
Cons: Harsh treble, annoying cable connectors
Positives - clean extended, balanced bass. Lacks the physicality of an LCD-2, but that's not unexpected.
These are large, heavy headphones, that I found surprisingly comfortable to wear when used with the velour pads. As reference, I have a small head, am not particularly sensitive to pressure on the top of my head, but am quite sensitive to pressure around the ear. For me, these were way more comfortable than I expected based on experience.
Build quality of the headphones seemed good - stock cable cover (not the cable itself) was already separating at the Y junction however (purely cosmetic impact but not a good thing).
These headphones seem to be generally well regarded, but for me there was one factor that made them unusable - the treble. Fair disclosure - I am not a fan of overly bright treble, however with the HE-400 something beyond simple brightness was happening - almost a resonance effect in the highs. The impact for me was that listening to the HE-400s for extended periods made my ears hurt (beyond simple fatigue).
In some other posts, I have read about "tizzy treble" being tamed by carefully tightening the headphone cable connectors (which have a PITA design). This could have been my issue, but if it was it's certainly a design flaw. I could have had a bad unit, or my unit may have sounded as designed - I don't know. I do know that I could not listen to them for extended periods of time.
These were known good HE-400s without previously discussed (and now long corrected) build issues.