Sennheiser IE 100 Pro Clear

I use these as in-ear monitors when playing drums and have just switched from the very popular SE215. The Sennheiser IE100 are much more comfortable to wear and don't work they way out of my ears mid-song as the old ones used to. Absolute pleasure to use. The sound is OK, nothing hi-end, but for monitoring applications that really doesn't matter. Very happy with this purchase and definitely recommended.

I use these for listening to music and podcasts during the day, In other words: Can't comment on on-stage monitoring performance.

Soundwise I can compare to a variety of full-sized headphones. From the usual Suspects, my favorites would be:
Sennheiser HD650, AKGk702, Beyer DT250
All these I consider to be fairly neutral (as opposed to e.g. a Sony MDR V6 / MDR 7506 which is nice, but not neutral).

The Sennheiser IE 100 Pro appear to be mostly neutral to me, too.
Treble is somewhat enhanced as far as I can tell, but not in a dominant way: They are not sibilant and not fatiguing.

So soundwise, I am very pleased. They offer a neutral, great sounding picture.
Soundstage / Instrument separation is very good for a headphone, especially in-ear phones:
The spatial origin of sounds seem to extend well beyon my head.

Replaceable cable is a must. As soon as those disappear, my money will disappear.

My biggest grudge with Sennheiser: Replacement part prices.
There simply is not justification for selling 4 cents worth of plastic foam for 40 bucks. No problem with profit margin but not three orders of magniute. (Looking at you, HD 650 earpads)

Cable for this thing: 40 bucks again. (IE40 cable)
I am looking forward to test durability with these.
Overall: Great product.