For me it's Megalomania on the Megadrive. The idea was unique and the gameplay was addictive. I'd love to see what modern graphics and online multiplayer could do to it.
Unlike Worms which got its million sequels, and even 3d variations like Hogs Of War, Cannon Fodder seems condemned to the past; which is sad as, if done properly, I could see a proper 3d version of Cannon Fodder being fantastic.
inb4 someone tells me that I'm an idiot that hasn't paid attention over the last 10-15 years and there's been N reboots and remakes already.