I recently got the BMCC 4K with canon lens mount, cost $2k. My 2 disappointments:
1. fan noise makes the internal mic useless for anything ( realize it is not meant for much except scratch, but when doing on the run interviews, it would be nice to have something useful.).
2. I though it would preform better at low light levels. I have not yet comprehended how example night scenes with available light are being captured, though I have not yet tested the RAW format. Working in low light is a requirement, and this has been sorely disappointing so far.