Excellent concept, comptetent execution.
I've never quite seen this particular take on a madness-like game. I find it immensely refreshing and quite fun to boot. What i would recommend making user-defined checkpoints, so that after performing one action they have time to think about the next. Perhaps make a minimum time between checkpoints, so that players can't abuse it. Next, as the down key has no real function, i would take out the rather annoying feature of having the timer run even when standing still, and replace it with the ability to advance time (while holding still) by pressing the down key. Even more, make it so that while you do this, you can dodge a few shots fired from an enemy (but not a salvo). This would work particularly well if you could combine this with the ability to predict enemy actions, even if only vaguely.
More ideas... hand to hand combat, for both the player and the enemy. Make it so that it seemed like a last resort, which it is. Maybe engineer it so that you can only take out an enemy after they try to attack you, as hank usually does in the movies. And add in enemies that spawn as the battle progresses, instead of having them all on the screen ahead of time.
All these ideas spinning through my head... i wish i could make them a reality myself.