I think these headphones are great. I'm coming from senn hd595 and also own a pair of grado sr225.
Compared to those two it is clearly superior in pretty much every way. Vs. the hd595 it seems to have more detail and texture and certainly more bass. Soundstage is similar. The dt990 is also very nicely built and really comfortable. A much richer, lively, exciting sound.
vs the grados the dt990 are more comfortable, have better detail and separation. Bass is maybe similar, perhaps the grado have a tad more punch but not as much detail. And I guess to put it simply since I'm not great at picking out details, the dt990 everything better. It will be hard to see which I pick to use in the long run as I really like the grado sound as well.