I have not played it against someone yet so i can only comment about the game feel and the levels i think. So levels has nice variety each has different looks and different gameplay strategy. In some you die instantly when you fall in the water, in others you fall from top of the level. Game feel is nice, you have a good control of the character. Only thing i felt can be changed is jump height. It felt short. Maybe tweak the jump.. or jump boost item? idk.
Regardless, congrats on the demo release!