The first, a 600 ohm, has fifteen years and still works perfectly. I changed once the velvet earpieces and headband the headband. These "parts" are no problem.
I bought it (250 ohms) for use on a laptop with an external sound card Creative Sound Blaster X-Fi HD Sound Card. I can only recommend to test this combination audiophiles.
For sound quality, nothing beats a try. I do not want to convince anyone ;-)
All I can say is that with the DT990 PRO, I do not feel any fatigue, even after hours of listening.
I enjoy the sound (of my FLAC): deep bass, treble not aggressive, very airy soundstage. The finer details of the recordings are viewed with great clarity but without any drought.
Lower quality recordings (or too compressed) are also ruthlessly unmasked ...
When I listen to my music with this headset, I do not feel completely isolated from the outside world (that means no problem I hear a door bell or telephone, important when you live alone).
I've read several times that the DT880 and DT770 were more neutral. The DT990 is considered more "punchy" but not excessively (imho).
Note: PRO is a hundred euros cheaper than the DT990 model (which also exists in a "Manufaktur" version with a choice of 3 impedances and custom finishes). Without dwelling on the differences between the PRO and the "normal", I simply point out that the hoop greenhouse a little more about the PRO (for a better fit on the head) and it has a coiled cable, style phone, handy for me, perhaps less so for others.
I hope that this advice will be useful.