The first section of the third level was hard for me, because i kept pressing space too late, or suddenly lost air momentum, or the next platform was just a tiny bit too far. That may be just me, but i just couldn't pass that section in a seamless way.
Turrets being able to shoot through walls is an interesting and unusual mechanic. The beginning of level 2 does it right, where I can clearly notice the turrets behind the walls i have to walljump, but on the other levels i was surprised to see i was being shot at through the ground or the big arrow walls. You could try to change the level design to make the deadlier sentries more noticeable (maybe with glass walls ? you decide), or give a wall-hack style highlight to turrets that are currently targeting the player.
Also, turret platforms being completely non-solid after level 1 is just deceiving, make them much smaller so the player doesn't have the incentive to jump on them.