Just the overall sound, they are the first decent pair of IEMs I have owned though. I always used to buy cheap ones before which would break after a few months and ended up costing me more than just buying a decent pair.
I can't compare them to anything else really, but I want to step up from them and seen as the 215s are good the next logical step would be the 315s. But i'm just wondering if going from the 215s to the 315s is a worthy upgrade, or if there is a better alternative.