My solution was to try out a few sets of longer tips that came with other earphones I've tested and I did find a set that allowed me to get a tight seal. The difference in sound was night and day. As I said, these can really sound great and they're a pleasure to listen to if you get the proper fit. They might not have quite enough bass for some folks who like a ton of bass, but I really liked their clean, accurate sound.
In some ways they reminded me of the $200
As far as comparing these with the company's more expensive M500s, I actually preferred the M200s sound, though the M500s are clearly more comfortable (comparing the fit of in-ear and on-ear headphones is a bit like comparing apples and oranges, however) and deliver more bass. The M200s are more forward (the sound felt more immediate) without being too bright; everything about them seemed a little tighter and more refined.
The M500s did better with hip-hop and techno tracks (Kaskade's "Atmosphere," example) and were also good for rock. The M200s are for someone who wants a natural, accurate-sounding headphone. I thought they did well with the Kings of Leon's "Supersoaker," a rock track that has several instruments playing at once and can end up sounding messy on lesser headphones. You can clearly hear each of the instruments without having one overpower the other -- or the vocals.
I suspect that in time KEF will provide a wider selection of eartips with these headphones that will help more people get a better and more comfortable fit. When the designers get the eartip equation right, these have the potential to be a four-star product. But as it stands, their fit and comfort level hold them back. That's a shame because they really do sound excellent if you can get a tight seal.