Generally find myself using these straight into my ipad when listening to podcasts or spotify, and for that, they are wonderful.  The sound seems full and complete for long term casual use.  Plugged into my pc for gaming and music, I run them into an Nad d1050, and they really shine there.
 
I switch between these and the Shure srh840's for casual non audiophile use, but mainly end up using these more because of the comfort.
 
They are rather cheap feeling.  Definitely not the best built headphones at this price.  But, on the flip side, they're light and sit so comfortably on my head, that I forget I have them on most of the time.
 
Oddly, I don't like the typical Sennheiser sound.  I've owned a pair of 650's for years, and maybe for lack of proper amplification, I just never got into them.  With that said, I like these, as they sound a little more alive and less forcefully even than my old 650's did.  Perhaps not as accurate, but I'll take fun over accurate any day.
 
They're a good recommend for people who don't usually like headphones.  They're easy to drive, comfortable, and the open back design keeps the ears cool and also keeps the sound from being pinned completely in the head...they sound more like speakers than headphones, which for non headphone people, is a plus.
 
They're not the best I've heard, or even the best I own, but I use them the most, because not everything in life is about music (though I always wish it could be).  For everyday tasks that require sound but some amount of consideration to the people around me, like movies or gaming, or even casual listening while I write, they sound good enough and feel great enough, that I use them all the time for anything I can rationalize using them for.

Heard these at a gaming convention.  Wanted to buy a pair riht there and then, but they were not allowed to sell them at the con, so I went to their site, picked up the black/gold version with a 40% discount.  Sixty bucks for these seems like I stole them.  Here's why...
 
They sound FANTASTIC!!!  I never heard the v1's, but I own a pair of sennheiser 650's, also a pair 590's, Audio Technica M50's, shure e4's.  I like listening to these more!
 
I'm not saying they're better.  I'm saying I like listening to them ALOT more than any set of headphones I've ever placed on my ears!
 
They have a very energetic presentation of music without showing an obvious fault in the audio spectrum.  The bass gets nice and big when the music needs it, but isn't boomy or excessive like the M50's tend to be.  They remind me most of the Senn 590's, with a very lively presentation, but a richer midband, and without the screechy highs I've endured with the 590's.  Another way they remind me of the 590's is their comfort.  These two headphones are the only two I could literally fall asleep wearing.
 
Unlike the 650's sorta blandly even presentation, the Siberia V2's sound big, alive, without getting too in your face about it.  They have energy without overhyping the bass or the treble to do it.  And I have the 650's hooked up to a Benchmark DAC1 USB, while the Siberias are plugged into my Asus Xonar's headphone slot.  I've done some opamp mods to the card, but the Benchmark is still the superior headphone amp, with the 'superior' headphones attached, and I enjoy listening to the Siberias.
 
I have noticed that, with some complex music, that the Senn's stay composed alot better, seperating instruments in the mix better, but I really have to listen to the mixes to notice it.  when I'm just listening for enjoyment, I prefer the Siberias.
 
I don't mean to imply anything except this.  Spending alot on the Senn 650's didn't bring me to the audio nirvana I hoped for.  The cans aren't my cup of tea.  they didn't endear themselves to me the way the 590's did in the past.  I guess I like a more lively presentation, and I don't want to say that they're bad, or that the Siberias are better.
 
But they are, for long periods of time, a VERY enjoyable set of headphones that allow me to connect to the energy of the music.  they haven't worn on me, nor have I noticed any glaring faults with them, especially for their price.  They're REDICULOUSLY good for their price, and a joy to wear for long periods of time, both for comfort, and for musical enjoyment.  They remind me of the Senn 590's, but richer sounding, without sacrificing the energy of the music.  But those headphones weren't too popular around here, and there's a good chance these won't be, either, but man to they make music sound alive!
 
My only advice to anyone who has ever looked at these headphones.  Do anything you can to try these out!  They are the real deal!  They sound better than they have any right to at their price point, and while I would NEVER claim they are the best headphones out there, you might find, like I did, that they are more enjoyable and bring more joy to you and your music than anything else you've tried so far.

Had these things for a while now, and still use them with almost anything that has a headphone jack attached to it.  My phone, my old iPod, my iPad, my pc, my laptop, and they always find a way to sound really wonderful.
 
I'm not gonna lie and say I'm some headphone guru.  I'm not.  But i LOVE headphones.  Cheap ones, expensive ones, gaming ones...i mess with them all.  I've owned grados, senns, sonys, denons, AKG's, Beyers...really could have bought a car with how many headphones I've owned in my lifetime (a house, if you include all the headphones my family and friends pass down to me).
 
Point being, I've heard alot.  Not all good, but most headphones sound good as follows...with the right input, on the right music, listening the right way...etc.
 
The Shure's sound good on everything.  I have yet to plug them into an input that made them sound bad!  They just make music...never forcefully, always relaxed and full, without any irritating edge or bite to the sound, yet always giving the impression that you can hear into the mix as deeply as you want.  The better the source, the better the music gets.  Key word...MUSIC...not headphones...cause they're always good.
 
I've owned more detailed and resolving headphones.  But they're far more finicky, and seem to do some music good, some bad.  The Shure's do everything well.  All types of music.  Ample bass and drive for rock, good sustain and warmth for vocals, and enough detail for piano and jazz.
 
I have a box in my garage that is filled with headphones.  I have exactly two pairs NOT in that box.  The first is a pair on Senn 600's, that I hook up occasionally when I feel like breaking out my headphone amp.  The second are these, and they're on my ears anytime I'm outside my listening room/office (sometimes, while I'm in there, as well)
 
Really no complaints can be made about these, for how good they do everything.  The only in ears I've heard that were better are the e5's, and they're just to big for me.  For the size, and every limitation the size would seem to impose, I've yet to do better than these for the way I like to hear music.  I forget they're on most of the time, except when my phone plays a song I haven't heard in a while, and I catch myself hearing something I never heard before...then I smile.
 
What I won't say is that they're the best for everyone.  While I think anyone would like these alot, some people like a more exciting, up front and present sound, so those people can probably do better.  But, for me, they've been glorious!