I've had the RE-400 for a few years now, but I've only started really regularly listening to it recently. I am now truly appreciating the balanced sound it gives. The only negative I can think of is there is a bit too much energy around 2khz, so it comes off as shouty. But, every other part of it sounds pretty much perfect to me. I like to experiment with EQ a bit, and I found that decreasing 2kHz a few decibles and increasing the treble above 8kHz makes this IEM sound top of the line. In fact, it now resembles the sound quality I hear from the Sennheiser HD 600. Truly an underrated IEM, and unfortunately I think people won't give Hifiman IEMs a chance due to their poor quality control reputation.