pretty cool already, i like the circle livebar, could look excellent with an overlay or something, like the quick charactermovement and animation,
for me, (but i play with arrowkeys because wasd is unplayable on azerty)
rightclick should be the slowdown(boost) and extra key maybe ctrl or shift for rocket
and make better button to play, it takes like 5 clicks to go into training
ps, topdown looks pretty good and lends itself to this kind of shooters,
you could make area's you have to clean, like when the waves is done, you scroll to other place and waves start coming again.