I'll preface my review with that I am not a seasoned audiophile, so I don't know all of the jargon, but I do appreciate good sound, and I like what I hear in these.   They are by far the best sounding headphones I have ever listened to.
 
Granted my collection of headphones is very limited.
 
I was looking for a closed circumaural design, primarily because I find circumaural cans to be the most comfortable, and I like the isolating effect of closed designs (less sound out to annoy others, less noise in to annoy me).

These headphones work very well in that regard.  I have occasionally even flown with them. Who needs active noise canceling, when these work as well as they do?  Though while flying, a portable dedicated headphone amp definitely helps.
 
The biggest negative with these is the break-in.  I almost returned the headphones when I first got them as I found the highs PAINFUL and piercing.  at first break-in didn't seem to help, but as a "hail Mary" I left them on for a couple of weeks playing music I enjoy and it did the trick.
 
These headphones are not neutral monitors for sure.  at the same time, I feel like their reputation for being overly bassy is a little undeserved.  often when listening to music I feel like using an equalizer to up the bass a bit.   That being said, I listen to a lot of 80s stuff where the bass isn't very prominent in the mix.
 
Overall, I feel like I got a set of great sounding headphones for a relatively low price.  I am happy with them.
 
If I knew what I know now when buying them, I may have opted for the 250ohm versions though.

I am not a seasoned Audiophile and not fully comfortable with all the terms used by reviewers here yet, so I am going to refrain from commenting on this soundcard in too technical terms.
 
What I will say is that Creative went all out with this board.  Determined to fix their poor reputation among audiophiles they threw quality components at this board, and it shows in the sound quality.
 
In the past with other sound cards from creative, system noise has been a problem.   This board is perfectly quiet.  With my ears I can not discern any noise/hum/pitch coming from the computer at all, regardless of conditions.  It probably helps that I have premium components in the machine that don't give off as much noise as cheaper computer components, but the sound card gets credit for being fully enclosed in some sort of shielded cover.
 
The card apparently uses a Burr-Brown 24-bit 192KHz delta-sigma stereo DAC.  This chip is apparently also used in high end CD players like Cary Audio Design's CD 306 and Halcro's EC800. The Op-amps are replacable if you like to tweak your gear, but the included two National LME49710 high performance, high fidelity op-amps sound great to me.
 
The line level RCA outputs on the back sound good to me, as does the dedicated headphone jack, capable of driving up to 300ohm cans according to the spec sheet.  With my 80Ohm Beyerdynamic DT770 Pro's the sound quality is fantastic, though I find that my comfortable listening volume is somewhere from 35-40%, so someone with higher impedance cans may find it a little weak.
 
I have not yet tried the digital output, but since it bypasses the on board DAC, I don't expect any surprises there.
 
My biggest gripe with this sound card is that in the name of sound quality a physical switch in the rear headphone jack turns off all other analog outputs.  I appreciate Creative trying to care about sound quality, but at the same time this is a huge pain.   What this means is that every time I want to switch from headphones to speakers, I have to crawl under my desk, and disconnect the headphones from the back of the computer.  This isn't just a pain, but I can see how over time this may wear out the headphone jack to the point where the solder joints to the board weaken.
 
To solve this I plan on getting a Schiite Asgard headphone amp and connect it to the line level RCA outs, as well as splitting the output with RCA Y splitters so I can still get sound to my speakers.
 
Drivers are rock solid.   No problems like we experienced back in the early Vista days with creative products.  Control menus could be better laid out and easier to understand, and a built in equalizer would have been nice (heck, maybe it's there somewhere, but I just haven't found it yet).
 
To sum it up, I think its a great value at $150 with a good enough DAC to listen to music on good headphones, at the same time as having all that EAX stuff on it for the occasional gamer.  too bad about the headphone out switch though.   That is REALLY annoying.