what about doom 2 and doom 3? those were spaced a ways apart weren't they. But I think the other games mentioned are on a much different catagory than say D.N.F. or how about Starcraft Ghost.
Actually, Prey was officially canceled I believe and then just announced again within a year of its release. Half-life 2 came out 6 years(?) after the original. We all know about Stalker.