Pros: Sound Quality, Detail, Sub-Bass, Crisp Highs, Huge Soundstage, Comfort, Build Quality
Cons: 10ft Cable which I hate and that's really it
Upon getting them the first thing I noticed was the build quality, its very good as you'd expect from HiFiMan and also how comfortable they are. I had other cheaper headphones but they weren't this comfortable, I can wear these for hours no problem at all.
As for the SQ its just great and I'm quite hard to please when it comes to SQ. Three things I look for in a good IEM is detail, good mids and a good soundstage so I was hoping the HE-400 could stack up. Now with the soundstage I knew they would be good being open-backed and man are they, very wide with excellent depth and good height along with great imaging and good separation. Now the mids are the meat of music so they have to be good and the HE-400 while not as forward as I like they sound great, smooth and warm with good detail just how I like it. As for detail that was my biggest worry because coming from BA based IEM's like the SM3, e-Q5 and BA200 they all have very good detail and micro detail. The HE-400 really surprised me with the level of detail, now they don't quite have the micro detail of most good BA IEM's but they're not to far behind, I don't feel like I'm missing anything in the music. The bass and highs are also very good with the highs being a bit bright but not to bad over all and the bass on planars I've heard is very good and the HE-400 is no different with nice punch and very good depth and rumble but these aren't true basshead headphones though.
So over all I'm very happy with the HE-400 and honestly I haven't really been using my IEM's since I got these a little over a week ago. They have good detail and a great presentation so if your looking to get into good headphones unlike Beats or even Bose the HE-400 is a great place to start and I'm already looking into getting the HiFiMan HE-500 because planar magnetic is the way to go imo.