Sine Mora is a side-scrolling shooting game dealing with time manipulation.
Metal Slug X
The Metal Slug games represent a high watermark for arcade side-scrolling shooter graphics, and the PlayStation port of X does not disappoint.
If you're interested in pure Galaga nostalgia, Galaga for mobile is a perfect port.
Metal Slug 3
Metal Slug 3 brings its signature run 'n' gun shooting action to Xbox LIVE Arcade.