In music: Imaging , bad. Soundstage, bad. It might be impressive at first, but its highly unrealistic. Imagine the soundstage of Q701 as a very wide thin wall that passes trough the middle of your head. Sounds that should come from in front of you, or behind you, or from the center, don't feel like they come from there, instead, they feel like they're cut into two pieces, and one comes from right, one from left. For example, vocal is never present in front of you, it feels like its singing from left and right, or from inside your head. That creates a weird soundstage where vocal comes from inside of your head, and instruments come from WAAAY too far away. Imaging I feel is bad in music. You can never pinpoint where the sound comes from. I might have been spoiled by the Ultrasone HFi2400 which is amazing in that regard, but after listening to those and then putting on the Q701, it feels like sound becomes very flat and two-dimensional. On Ultrasones I can even distinctly say where the backing vocals are standing in relation to each other. Even my Sennheiser HD438 has far better imaging and more realistic sound stage than Q701, and those are 100$ closed headphones.
Other than that, Q701 do sound very nice, they have nice natural sound, pretty neutral, highs might be a little boosted and bass might be light to some, but I find it works well for all genres except those really bass heavy ones. If you want a movie theater sound, then these are not it.
In games though, they are amazing, WHEN paired with a soundcard that has Dolby Headphone modes. Somehow their overly large soundstage works very well with Dolby Headphone effects. That said, I'd pick Ultrasone HFi2400 over them any day, for any purpose. Check those out. They also sound far better than HD598. Don't know about DT990.