The problem that some people have expressed is that they feel that their style of mapping simply has no place here, or that they simply get sick of being pissed around. It happens. It's also an annoyance that a lot of mappers are flat-out lazy, and the fact that this laziness is enabled is what puts off those who pour a lot of time into a mapset. Again, it mustn't be a good feeling for excellent mappers when they try their best, only to be stuck in a queue behind slop. There's only so much of that that people can take.
Guest difficulties are also becoming quite a serious issue and it should be up to the mapper to decide on one or two guests, instead of asking a load of people for guests, mapping one difficulty on their own and calling it a day. It's even worse when there are more than four maps, with superfluous guest difficulties.
As for unenjoyable maps, it's reasonable to refuse to rank something if it has a bad feel, even if it is technically rankable. Thorough modding can suggest ways to make patterns feel more comfortable or to tone down overmapping. Additionally, if patterns outright ignore/plough through important musical elements, then they should also be changed. It may be worth having some emphasis on the map emphasising the music in a logical and consistent way, so that there's a continuous feel throughout.
DEEDIT: I agree about the mapping community catering to experienced players. On several occasions, I've mentioned that, just because we as committed members of the community have been conditioned to certain quirks, it doesn't mean that these quirks should become standards. Players who are just getting used to playing harder mapsets could be turned off completely by some of the habits which mappers have acquired. There's "evolution" and then there's losing sight of what is accessible to as many people as possible. This game is becoming big and osu!stream is on its way to gaining some serious headway in the App Store. Sooner or later, more casual players will be drawn to this and osu! may become less of a cult, so we're going to need to consider them more. Even making easier easy maps would be a start.