Possession = Infection? By What? That leads from virus to parasites (like Headcrabs) and through X-COM Apocalypse to the Micronoids which leads to further parallels with the "Black Oil" from The X-Files.
If one sees zombies as a alien experiment to create cheap human soldiers and slaves using the available material, then fast zombies and eventually zombies smarter zombies make sense, possibly ending with zombies smart enough to use tools and weapons. So you end with Doom-style zombies capable of using guns, and maybe even tactics (minus demoniac possession).
Another avenue of research, of course, would be the Resident Evil path - mutate them into more and more gruesome and powerful mutant monster things.
Then there's the Cyber-Zombie route, which is either "reviving" dead bodies with cybernetics (Universal Soldier-style), cyborging people into zombieness, or sticking cybernetics in already-existing zombies.