fwiw: When I auditioned these, the pair the store had me try on was considerably worn already so I imagine that it had hundreds of hours on it already. It sounded glorious. But when I first listened to my newly bought pair, I was like "What are these, this isn't what I paid for..." --- so the sound does change significantly with burn-in on these.
Even the store owner told me not to be surprised if the sound seems too thin at first.
Based on what I've read online, the point at which the RE400s really open up is after around 200 hours of use. I don't know if I've gotten to that point - I don't really count the hours - but the sound of my pair has indeed changed since when I first bought it.
Though I agree that if you still don't like them after a few more days of use, then maybe you just don't like them