I can't remember any problem during the upgrades of the recent years. I often apply partial updates through `aptitude` on a weekly basis, and full upgrades once in a while (maybe monthly). There were some rough times long ago, but I think it was related to the transition from initrc to systemd: for a major change like this, it's would be surprising if a testing release was perfect.
I don't think I ever had problems as acute as having no Xorg or alsa. If several occurrences of this kind had occurred, I would call my OS unstable.