I played the game 16 hours since release and I love it. There are several bugs but the game is in a playable state and it's a lot of fun.

But there are things that are vital for coop with strangers :

The most important thing is the possibility to ping ON THE MINIMAP. It can help telling people where they need to go or what door they should open next. You could do something like in League of legends with many pings like "on my way", "retreat", or "hold" when holding the ping button. (and keep the basic ping on single tap)
A basic example is when there is a chest with not taken content. I wish I could ping it without going to the area again. It could help to ping which door to open too when there are several choice, because going to the door you want to open and then ping is often too late and another door has already been opened.

You should consider adding the possibility to text chat with others too. Sometimes I want to tell my team basic strategies and it's not possible. Like going eco early game and don't spend all ressources when we are going to change area in like 2 maps. I know you plan to add console support so at least a simplified chat with few possibilities like "I defend this area" or "eco" or "we need more defenses" could be a great start.

Playing with strangers is playing in super hard mode when you can't communicate and it's something that needs improvement if you don't want to see people leaving the game after few weeks.

Hey, thanks for the feedback. We've already added improved communication tools for multiplayer in our feedback document for the production team.