Just as this is a relevant thread, I thought I'd share my experience.
I've had Etymotic ER4 headphones for the last seven years, until I lost them recently :-(
I always thought that they were very good, but maybe a bit overpriced.
Looking for a replacement, I did my research and decided that I'd go for Shure SE215. Recieved this morning, tested on various songs I know very well. They are being returned.
Apart from being fiddly to get into place, both the foam and rubber tips are inferior to the ER ones, meaning that it's more difficult to get the necessary isolation.
The best description I can give to the sound is artificial, especially on the low end, a bit lacking in the mids, and a bit harsh on the top end.
I guess I'd been taking the quality of the ERs for granted.