Overall, I am not a big fan of IEMs. Mine sound fine, but I just can't get comfortable with them inserted into my ear. I replaced the OEM tips with Comply tips, which I find a bit more comfortable. However, I really prefer the comfort of a regular headphone, either on-ear or over-ear, for longer listening sessions.
Naturally, this is a matter of personal preference. I wonder how custom-fit IEMs would feel, but I really don't use IEMs that frequently to make such an investment.