Jonathan Soderstrom's Ad Nauseam 2 is a space shooter game that provides an overwhelming synesthetic experience: start playing and you'll find yourself restarting over and over again as you learn to master its maneuvers and get drawn into its psychoactive swirl of color and sound. Your podlike ship shoots two kinds of energy blasts and can also emit a kind of gravity pulse that beautifully blows away debris around it; your enemies begin as a pair of crudely-drawn semi-happy-face blobs that grow into menacing starfishes, turn into ASCII robo-ships, then ramp up to a final boss battle. Ad Nauseam 2 is one of several indie games available on Soderstrom's Cactus Software site, including Burn the Trash and Shotgun Ninja, that work with ancient arcade and first-gen console forms like the shooter and platformer, ramping up their audio-visual intensity, twitchiness and formal ingenuity for a hungrier generation of gamers. But other Cactus games are more contemplative, playing with narrative structures and standard expectations: for that kind of head trip, try out the Lewis-Carroll-esque Psychosomnium, which presents a world in a dream, or the starkly existential explorations of Mondo Medicals. - Ed Halter