Just received these today. I had no intention of buying them originally, but when I saw the sale price, I couldn't resist trying out a new closed-back, as someone who is ultimately a fan of closed-backs over open-backs.
I'm impressed with the sound. I was concerned I might find them too bright, but they are not. They are brighter than the usual sound signature I prefer, but they are not too bright and I am not hearing any sibilance with treble-heavy tracks, like I usually do with headphones I reject for brightness. The bass has a decent punch, and the soundstage is decently wide for a closed-back and doesn't sound that different from my Sennheisers. This is the first closed-back planar that I've actually liked. And like my Sennheisers, they are sounding great with every genre I throw at them.
My main complaint would be the poor isolation, which seems to be a theme with Hifiman. They need to figure out a way to make a closed-back that does more than just slightly dampen external noise; the main reason I prefer closed-back is the isolation, and this ain't it. It's better than an open-back, but only slightly, and if I'm going to make these a daily driver they will need more isolation capability than this.
That said, these are the best closed-backs I've heard in a while, so I think I will hang onto them, while still on the lookout for a more isolating one.