At first, the art and comics are awesome, but the amount of time you have to defend Grandma is too much.
I think it could be a terrific little game if you changed some of the game design features
like making items do more damage but there are less of them, reducing the time to a maximum of 2 minutes, adding more challenging trajectories for items
and if you also added a mech that you can drop "good" items yourself and it makes the granny rage scale go up - that would be perfect