The levels and balance are all work-in-progress. You can't buy and upgrade weapons and abilities in demo version. Only straightforward action. 2 players co-op is available, so try it.
There are 3 levels in the demo. Full version will feature 30 levels in 10 environments. Current balance is a work-in-progress thing.
Since Chaos Domain is a platformer game, developers encourage you to adjust the controls in the Settings menu, so you could feel comfortable. You also can use your gamepad.