I can't say a whole lot about gameplay itself since I haven't managed to join up with anyone, but there are things I can say on the technical side.
For example, I have noticed you keep the mouse cursor visible at all times, allowing you to interact with interface elements easily. However, when I tab to other windows then back in, the mouse cursor will disappear, making interface harder to interact with. May I suggest Tab also toggling the cursor's visibility as well? That way it may not be an issue.
Maybe allowing a key to have the game focus on the chat's textbox could be useful too if you want to talk quickly without locking the interface entirely, which I imagine would be useful when in imminent danger.