I'm sure people have addressed this in the thread, but these are a few of my complaints with competitive so far:
If people leave mid match, in most cases, you basically lose. The game still takes rank from you. Despite the fact that it isn't your fault your teammates left.
In assault and its variants after a match in the case of a tie, a coin is flipped to decide which team will attack and which will defend. In a normal assault the attacking team has around 3+ minutes to attack, during the coin flip you have 1:40, which I feel is a bit unbalanced.
Personally, my first 3 matches I had my teammates leave so I was already down 0-3 for placement, and I had to wait 3 rounds in some cases just so I could at least get a rank for a loot box.
So far it's okay, but I think competitive still needs some work, hopefully sooner rather than later, as right now it's pretty disheartening.