The thing that works the worst in the game at the moment has to be the competitive matchmaking. Long queues are imo fine, but not game after game failing to start. As I haven't seen any developer or such mention that it is any kind of priority to fix it, I want with this topic to make my voice heard that I find it to be the highest priority. Partially because it is my favorite mode, partially because I find it to be the most broken thing in the game.
Every day that it is broken the more damage is done to the reputation of the mode (and the game). Damage that will take a long time to repair once fixed.