I was into Korean entertainment since 2005 but have been out of the circulation for like 2 years now (focusing on KAT-TUN :D) so I can't really provide much detail but that despite the fact that they produce successful artists, they're management style is bad/shady - like they run them to the ground with work but they take the bigger share.

My favorite K-pop artist is Shinhwa. They were recruited, trained and launched under SM Ent but has moved on since 2003 - am I glad! They had legal battles with SM as well after they refused to sign a second contract with the company.