I liked the fact that you have to quickly think about which tool to use (bullets or shield) and this is a great gameplay gimmick.
However, I think the game is missing some sound effects or music that could really raise the bar!
Also, as someone else in the comments mentioned, I think there's a little too much delay between the shields and the shooting but maybe I'm wrong and I just need to gitgud :P
Other than that, good idea :)