i have been listening to HE-400 since yesterday. let me answer a few questions
1. In terms of the build quality, it's exactly the same as HE-500 and HE-6. Personally I can't tell the difference at all.
2. The blue color actually looks pretty refreshing. I thought i wouldn't like it, but i kind of do.
3. The first thing people will notice about this headphone is the bass. I have heard almost every single Hifiman Planar headphone, and they always stay just a little bit light on the amount of bass (although they do hit pretty deep). HE-400 is different. It's the first Hifiman headphone which will grab you first with its bass performance. It's definitely tuned for Rock, Electric or R&B music. I can't help myself to compare it against LCD2 which has fantastic bass performance. I am not going to comment on the actual performance yet until I listen to it for at least one week or two.
4. I have been driving it directly out of my iPhone4, and getting surprisingly good sound. The volume is at 80%, and everything you expect from a planar headphone is all there. Yes, it definitely performs better with an amp, and I am always against not using an amp especially with an Ortho. HE-400 is changing my mind. It gives you an option to drive it directly out of i-devices, and not making you feel that you are missing something. It's quite awesome actually.
5. How does it compare against HE-500? well...HE-500 is still superior when it comes to transparency and clarity, but HE-400 offers better bass impact and is much easier to drive. After the recent price drop on HE-500, it is considered as the best value on the headphone market right now, and i think that HE-400 just took over the crown in terms of value.