Summary: I like them. They are not ruler flat or reference grade but they are fun. Much better than my HD-681. I like them better than my HARX900 but not as well as my Senn HD-439 or HD-598. I'll be ordering DT770 velour pads. Got these on your want list? Go for it!
Summary: No it's not flat by any chance and it may need a bigger soundspace but I have no love for semi-open headphones. It's as big as a soundspace you may get on a closed headphone.
But it's very "listenable" or rather, enjoyable. It doesn't disappoint in any genres or even gaming although ... yeah.
Pros: Punchy bass with the right amp, yet not loose. Absolutely enjoyable.
Cons: The pads will tear in no time. Oh, maybe 300ohms. Design is very dated.