mdadm and associated init scripts was the dealbreaker for me

they broke the initscripts so array assembly didn't work correctly - not even the same as the installed man page stated

they had mdadm version 2.x (has significant flaws) for YEARS after mdadm 3.x was accepted into debian - YEARS - even after multiple users making clear what the problem was in bug reports

a user even made a patch and a ppa which fixed things but still they didn't pick up on that for a year + as i recall

and they broke/removed debian's PERFECT support for installation onto md raid

other stuff i've honestly forgotten but i swear there was more

oh! oh! wait, also the STOPPING THE BOOT PROCESS TO WAIT FOR YOU TO PRESS A KEY if a drive needed an fsck!!!!! what the f....

(don't understand why you were downvoted, good question)