
I'm also a big fan of multiplayer co-op. Not only against other users, but missions with AI opponents maybe? Often time missions against other users just turn into free-for-all, but structured missions with different objectives might be a lot of fun against bots, with different levels of difficulty.
The different game modes might be a good nice price point too. Standard game modes for regular users, but the more advanced game modes for paying customers.
just a suggestion, great job so far btw, love what I'm seeing