Nice concept,
and i like the progression idea where you start on foot get a few upgrades and then can get inside your mech.
Too bad that it's unfinished as you said :(
but what's there is cool i like the NES style sprites and the color palette, cause i imagine that if you plan on adding more areas you could have them have their own specific palette and such, the directional aiming when in the mech is also a nice touch,
the one thing i feel is a bit weird is that since you put Up as Jump, when you're in the mech you constantly jump around when aiming up.
Other than that it's a solid prototype and it would be cool to see where you take this if you plan to keep working on it.
well done :)