couple levels in the demo seem solid! I like the different weapon types - they all feel 'just right'.
if there was a way to lock your aim, like in Super Metroid, that'd be pretty great - and if there was some way you could avoid the Contra trap - where you have cool weapons, until you die to the boss and then you just have to finish the boss fight with your boring old gun - that'd be rad.
I'd pay a couple bucks for what you've got in the demo alone though - can't wait to see this released and play through in co op!