Honestly, there was a part of me that was worried that these headphones would not be the best pair to own after the issues that I experienced with the prior generation of them: the WH1000xm3. The main issue that I had? The build quality: the plastic around the headband snapped due to a flimsy connection, resulting in me having to tape both headbands together so that the headphones don't fall apart on me. I tried several alternate brands to see if they would work, but they never came close to giving me the same level of satisfaction while wearing them as the WH1000xm3 did, even with the taped headband taken into account. So I decided that the best replacement for a Sony headphone was another Sony headphone, and I invested in the M4, which succeeded the M3 last year (as of this writing).My initial thoughts were as follows: the headphones were a definite improvement upon the originals, retaining what I liked most about the original headphones (largely the overall comfort) while also improving the headphones in other small ways (especially in regards to the special features-the M4 are way more feature-packed than the M3 were, incorporating many elements that are being found on most other headphones these days). My favorite thing that was fixed, however, was the sound quality. You see, the original sounded amazing, and honestly sounded better overall than the likes of Bose and Sennheiser, which I have tested as potential replacements for the Sony headphones. And that is despite the fact that the headphones have a relatively small 40mm driver inside, instead of a more traditional 50mm driver. However, the one minor issue I had with the M3 was that the low frequencies were heightened a bit more than I would have liked, making songs sound a bit bass-heavy even when the EQ was turned off (the only way I was able to fix this was by setting the EQ to 'bright', which isn't ideal since the EQ does degrade the battery life). With the M4, Sony improves this by tuning down the low ends, resulting in the headphones having a very flat frequency response, which in turn results in every song having a much wider sound stage than the M3 did (and almost making them sound as good as the various open-back headphones I have tried, including the Sennheiser 650, which is my personal favorite open-back headphone).In terms of the special features, I think they were implemented quite well in these headphones. The noise cancelling is exceptional, much like it was on the M3, and the transparency mode is somehow even better than it was on the prior generation headphone, sounding a lot more natural and less tinny overall. The auto activation of transparency mode during conversations is fantastic, and enables me to talk to people naturally without ever having to remove the headphones from my ear. This also means that I don't have to awkwardly tap my hand on the earcup with the M4, either. The DSEE Extreme audio enhancer really helps to make music sound a lot more full, even when using devices that don't support the LDAC wireless standard. It isn't as good as listening to lossless files wired, mind you, but it is still an amazing feature that helps to take advantage of the flat sound stage and frequency response of the headphone drivers.Now, this isn't to say that these headphones don't have issues, mind you. The auto-pause when removing the headphones from your ears is very much a gimmick, and doesn't always pause the song (and may even resume the music before you have a chance to place the headphones back on your ear). Since the headphones use a light sensor to tell if you are wearing your headphones or not, it means even a simple shadow can cause the headphones to think that they are back on your ears and restart music playback. It is quite obnoxious, and it is best left out. Another, more minor issue is the touch controls. While I personally have no issue with them, I know that there are many people that don't like them whatsoever. So I will just make a note that they are still here, and they work in much the same way as they did on the M3. Finally, I should mention that the flat soundstage, while amazing for my listening experience, may not be for everyone. Bassheads in particular would likely prefer extra pronunciation on the lower ranges. And while they will never be quite as bass-heavy as the Skullcandy or Beats line, the EQ can still bring the bass levels up quite a bit, using a 'clear bass' slider that reminds me of the slider on the Skullcandy Skullcrushers: raising the bass without causing distortion.Overall, the headphones turned out to be quite an exceptional pair, especially when it comes to listening to music during commutes. The great noise cancelling, beautiful audio, and fantastic transparency mode definitely make these headphones a winner in my book. And the app only helps to improve the flexibility of the headphones, allowing for many different features to be unlocked. And while these headphones certainly have some issues (no pair of headphones are perfect, after all), I think the benefits more than outweigh the issues for me, and put these at the top of my list of best closed-back headphones that I have worn. Hopefully Sony will continue to make amazing headphones like these in the ears to come.