Jamestown by Final Form Games, 

Jamestown is a top-down shooter game that's probably unique in setting: an alternate history in which the planet Mars was colonized in the early 1600s. The English and Spanish vie for control, with the English protagonist eventually unveiling a conspiracy perpetrated by the "Conquistador", leader of the Spaniards.

Jamestown contains five different stages that follow the narrative sequence, increasing in difficulty as one progresses through them. There are also a number of challenge exercises independent of the narrative. Difficulty ranges from "Normal" (immediately achievable for the new player) to "Judgment" (where mere survival past the first few enemies could seem miraculous) - finishing the game is only possible at a minimum difficulty level of "Legendary" which, probably needless to say, is a nontrivial feat. There are four different vehicles to do battle in, progressively unlockable and each with its own set of weapons. Common to all is the "Vaunt" ability, which can be activated after collection of a certain quantity of the coins that fall from enemies, temporarily absorbing all incoming bullets and doubling damage and points scored.

Sam's Protip: Pressing the Vaunt key again while already in Vaunt mode will re-trigger the bullet shield, potentially saving one's life at the cost of future points.