Pros: Balance, imaging, speed from top to bottom, mids
Cons: High roll-off, no air in the bass
First of all, I don't think we should be comparing these to anything else but in ear monitors (IEMs), and generally in the price range. However, my only experience is with Sure SE 110s that I used for over 5 years. Those were about $99, and I got the 425s for about $270. I've now had them for about four months, and have gone through the slightly disappointed stage which seems to occur for a lot of people with a lot of headphones. No matter how much you read before purchasing, it still takes time for your brain to get used to a new sound signature. These really blow away the 110s in every way. They have energy, speed, focus and simply amazing imaging. I can't say the last part enough. It's not soundstage, per se, (because there's not much air) but rather the ability of these phones not to get bogged down with complexity. They just keep up, keep up, and keep up.
So, as others have noted, the bass tones are all there, and in fact I've noticed these IEMs are great for rhythmic music based mainly on acoustic instruments and vocals ranging from jazz to funk, reggae, to many kinds of "world" music. Also baroque music and small to medium sized classical ensembles sound great. This is because they really neatly lay out the different textures well. Marvin Gaye's remastered "What's Going On" for instance, is fun to hear. On the other hand, music that tends to be a bit dull and lacking in rhythmic or tonal variety to begin with might sound even more dull on these.
Moreover, the mids are great: smooth, musical and accurate whether you're listening to vocals or basically any other acoustic instrument. After all most acoustic music takes place in the mid-ranges. The main thing lacking is the sparkle on the high end, but even there, I would hesitate to say they have no highs. They can make some music sound pleasant though, where my Grado 80s (old version) become grating.
I think technically they lack some treble, but the roll off is nothing like the 110s, and since the sound is going directly to your eardrum, the dampening of piercing highs is not such a bad thing.
If you're really into genres that use a lot of what I call 'artificial' highs and lows, you would probably want to avoid these phones. They are also not amazing for large-scale orchestral work, and can at times be a bit boring for non-acoustic rock. I don't listen to any of these genres much, except for some hip-hop** and orchestral music. In both cases, you still have a great musical experience, but not to the level of good $300 over-ear phones, that's for sure.
They sound significantly better, as can be expected, with lossless and high bit rate tracks, but are very sensitive, and so don't do well straight out of the computer jack, even making amping a bit difficult. I use the Fiio e10, which is fine when listening at moderate or high volumes, not necessarily low volume though, as I get buzzing from the computer (Lenovo thinkpad) when it's charging. I also have a Music streamer ii dac and schiit magni amp, which do open them up a bit, and especially on high bit rate tracks show off what these IEMs can do. They are elegant and have excellent instrument imaging and separation, for example. This combo also brightens them up, which is good. You still can't listen on very low volume, however, as you'll probably get some channel imbalance.
They are a bit annoying with phone calls, because as they don't have phone capabilities (without a cord upgrade), you have to take them out and reinsert them each time you get a call. It can affect your relationships negatively if every time you answer the phone you are annoyed--both that you had to stop listening to the music, and because it takes a few seconds and some effort to put them in and remove them each time.
Conclusion: These are fine for acoustic music, which in my opinion, is essentially what music should be. The imaging might make them good for electronic music, too, but bass heads won't like them. But the advantage of these is the external noise attenuation, portability, and sensitivity, making them great for portable devices. With these on my daily bus ride in Tel Aviv, I can block out virtually everything except the vibration that comes up through the seat from the bus itself. Plus, in a hot climate you don't want anything on your ears when you're on the go, not to mention that some phones are just plain heavy, and as a backpack carrier, I also don't need extra weight. I briefly thought about selling these and getting Sennheiser 25ii headphones, but backed out due to my own portability concerns. Probably a toss up, with the se425s coming out a bit on top with respect to mids, imaging and balance, but 25iis, to my experience, having more bass impact (but not more bass tonality) and better high extension.
**If you actually want to hear the words of the hip-hop, these can help you with that, as they're quite detailed and can show you where there are several voices going on at the same time. They just won't give you anything like a club feeling because of the lack of air in the bass.