If Red Dead Redemption had been released on the Super Nintendo and hadn't looked like Sunset Riders, it might have looked like this instead.
This is Sombreros, a top-down shooter where you shoot Mexicans and collect their hats. It's even got a "dead-eye" aiming system!
You can download it here, if you feel like you should accomplish nothing other today than to amass a vast pile of tattered, bullet-riddled sombreros.
If you like what you see/play, it's part of a larger project called Action 52, compiling a ton of other retro-inspired games that is an amazing read in its own right.
Quick Sombreros Update [sniper diplomat via Rock, Paper, Shotgun]