Pros: Comfort, price, versatility. Great mids with powerful but warm and pleasant lower end.
Cons: Music performance drops as dynamics get tighter.
Have had these for almost two years. Though I'd at least write a few basic impressions.
First, the intended gaming and media use:
Well, I have to say I've found them excellent. Voices are clear, environment sounds are crisp and the lower end does subsonic rumbles and concussive thumps equally well. The phones actually still make me check if I have left my external subwoofer turned on from time to time. Headphone surround with the included sound card and drivers works decently, though I haven't had much to compare with. Borderlands 2 sounds open and wide, Bioshock 2 sounds confined and eerie as hell. They are comfortable enough for a weekend of Civ 5. DiRT 3, GRID 2 and Shift 2 have worked well without making engine sound annoying.
There are probably other gaming phones that sound about as good in the price range, but I haven't tried any that come close to the Siberas when it comes to comfort.
Over to music:
Gaming sound is a lot about high dynamic range, and with music I think the phones show their weakness at the other end. As the soundspace fills up the soundstage and separation go away. So, in my opinion they are not really for big rock and pop productions or for metal, hard electronica and other loud genres in general.
But, I think they really shine with more intimate recordings. The kind where you want a room rather than a stage. Vocals and acoustic instruments benefit from the mids and warmth in the lower end. Regina Spektor and Natalie Merchant sound as good as Leonard Cohen and Tom Waits. For club/electronic music I've enjoyed listening to chill/trip stuff like Air, Massive Attack and Portishead, and I think the bass works really well without taking over too much. Not much of a jazz or classical guy, but from what I've listened to I'd say small sessions and chamber music/solo/quartet performances work fine as well.
Some sort of conclusion:
I've talked a lot about mids and bottom, and those are the strong points to me. I'd say the sound is crisp with a dark sweetness. Honey roasted, maybe? :) The treble could be little stronger, but there are no real flaws there to my ears.
I haven't tried the phones with a proper amp, and as I feel they get muddier with portable devices and enjoyable with half decent sound cards and regular hifi headphone outputs it could be that a little more power could help keep those 50mm drivers in check even with louder music.
I've written this with the price in mind, and I think they are a bargain that rivals more expensive phones in the areas where they shine. With the retractable mic they make a practical and affordable all-in-one solution for all desktop needs like gaming, casual music listening and Skype calls.