My iem experience is almost not existent, mostly due to comfort...I've always had over ears (I've got K550s now) and the only decent iem I've tried is the se215. I found the very low mids a bit overbearing at times, probably around 250-300hz, giving sort of a bloated feeling. I really like how my K550s sound from about 200hz and up. I like where the mids are set, which to my ears is just north of neutral, hardly enough to notice. High mids and highs are good, less a spike at around 9000hz that I had to eq out if I want to listen for a long period of time. I'm sure you guys know know that AKGs aren't exactly known for their hefty bass reproduction...
Sound signature I like/seek... Smooth highs and high mids, lots of detail, but not overly bright, very slightly emphasized mids (mids are most important to me, so I've got to have good detail in this area), and substantial, but not bloated bass. I like powerful sub bass, only if it's tight though. By around 250hz though I like it to be just north of neutral, otherwise it just feels crowded.
Hopefully that helps...I haven't been in the audiophile community for very long, so my terminology is somewhat limited. Let me know if I missed anything
edit: I missed something... I listen to quite a few genres. To name a few: Classical, acoustic, shoegaze/post-rock, occasional classic rock, and some indie stuff as well (or whatever the fleet foxes, bon iver, iron and wine, etc. would be considered). Never metal, hip-hop, rap, or pop.
