These IEMs are incredible for its price. Have had them for about a year now, it is not thing of recent hype.
Changed cable and tips (would not recommended crystal copper cables, because highs are majestic already and the sound turns too crispy for my tastes). Regarding tips, JVC Spiral dots are working the best for a lot of users (me too).
Being honest, I don't have too much experience with real expensive IEMs (never tried 800$+ model and never owned 400$+), but the clarity of these is clearly hard to beat in their class (and a lot of more expensive options).
The bass is very good and multifaceted (from a little bit enhacement to a real bass bomb using red back filters and correct front filters). The mids are very good too. Male voices a bit recessed and very natural, female voices a bit forward.
With this, I honestly think that most people would have all they want in a hard-to-beat pair of mid-fi IEMs, and of course, the filters can always be changed to look for a different sound signature.
Cons: Not the best cable, not the best tips. Some people has had moisture issues (I did read it in head-fi too), but I use them every day in Barcelona (with frequent humidity indexes above 80%, raining weather, sunny weather...) and only noticed sound change once, after running and sweating a lot on a sunny day. But after 5 minutes with the affected front filter out of the IEM at home, the issue disappeared. Finally, some people see the mmcx cable connection as a fault (it is fussy, yes) but I consider it a good thing due to cable changing turns into an easy operation.
The base sound of the A4s is very very good and a real chameleon, due to filters. They can be changed to my linkings and I stopped using a couple of other IEMs I had reserved to Jazz, classical and acoustic music (JVC HA-FXT90, RHA-MA750, Advanced Sound S2000 and Shure SE425, which I never really liked because poor highs but are very relaxed).
As final words, I have been looking for another pair of IEMs under 250€-300€ to improve the SQ but after listen to some of them, I have no clear choices and decided to stay with A4s (looked for iBaso IT03 too, as many people says that they have something special apart from SQ, but I have not found them in any store in Spain or the European Union and, being honest, I don't think that the sound would have improved remarkably if that was the case).