Well, a lot of things really. IEMs are different to regular earbuds in the way that instead of one speaker in the shell that does all the work, there are several smaller ones that are tuned to a specific frequency of the audio spectrum, which means that the audio engineers that make these can focus on making each of the smaller speakers sound good in their specific range instead of trying to make a single one sound good over the entire audio range.

What I love about these specific pair of IEMs is that they got a pretty great soundstage for being earbuds, and they are absolute beasts when it comes to clarity. The buds are super well balanced across the entire spectrum, and no part feels bloated or "tinny". That combined with the super great clarity makes it absolutely dreamlike to listen to, being able to hear the "vibrato" of guitar strings as they linger after a chord, or the great bass riffs of songs without having the bass frequency spectrum being obnoxiously loud and bloated. I was completely shellshocked when I first listened to them.