I'm pretty sure Snatcher is longer than 30 minutes, but I know you can beat it in a couple hours at least. I've never beaten the game myself. Mainly because I started played then stopped until I found a Justifier. Then once I got a Justifier I never found the time to go back. Space Adventure Cobra is supposed to be another game with a similar playtype (also on PCE and Sega CD) if you're into those games. I highly recommend CDRs though.