If you have fond memories of the light gun-equipped arcade machines from the '80s, then you'll be very familiar with how Gunroad works. The screen scrolls automatically as enemy soldiers pop into view to shoot at you, so it's up to the player to take them down quickly while there is still a window of opportunity and an element of surprise. Retaliate slowly, and you'll lose a few points of health and get that much closer to defeat.
Mouse controls are used for light gun emulation here - holding down the left mouse button allows you to fire your gun continuously, and pressing the right button deploys a smart bomb to clear the screen of all normal enemies (bosses will receive heavy damage). Reloading your weapon is done automatically whenever your gun is out of bullets, and shooting at medikits or chocolate bars will restore some of your health.
Gunroad comes included with two difficulty settings, but even on easy it will take a bit of effort to clear all of the game's four stages. There are two files to download from the official site: gr_full.lzh allows you to play in full screen mode (may not work for certain display cards) while gr_win.lzh will display everything inside a tiny 320 by 240 window.