In short these are quite awesome, they do however leak sound.. those around you will know what you are listening to. But since they are open headphones this should come as no surprise.
How do they sound, very good. highs (high-hats and similar instruments) can be a tad sharp sometimes, but not to the extent that it will cause you to clench your teeth. Bass has a slight emphasis, not much but it is there, just enough to make them sound lively and not clinical.
The DT-990Pro comes in different impedance “models” (32/250/600) the 250 and 600 ohm models will need to be amped. There is no question about it. They are not picky about what you use to amp them with, in this regard they are quite forgiving.
Build quality is very good, the only plastic is the “guard” on the cups and some protective cover on the cup hinges other than that… it is all aluminium, and the comfort is good, they are a bit tight for me (but I have a bit head) but not so much that it is uncomfortable. It is just noticeable. The cups and pads provide ample room for your ears and the depth is just enough so that your ears will not touch anything.
Price, these can now be found on amazon for 145$ (US) and for that price they are a steal and will most likely sound better than any other sub 150$(US) set of headphones you can find.