Left 4 Dead, House of the Dead, Dead Rising, Resident Evil, and, to some degree, Dead Space are all marketed as zombie games. I meant to list them for completeness, but I was more interested in the games not really marketed as such but feature Satan's Unholy Army anyways.
It made me think: This doesn't seem to happen in movies. Either it's a zombie movie and it has zombies in it... or it isn't and it doesn't. Can anyone prove that wrong?
And RE: Half Life 1 vs 2. I never thought that there was much of a genre shift between Half Life and its sequels. Rahter that there were genre shifts within each Half Life game. You go through puzzle sequences, sneaking past alien monster sequences, vehicle sequences, shooting monster sequences, shooting army guy sequnces, sneaking past army helicopter sequences, etc thoughout each of the games. I also don't recall HL1 being any scarier than HL2. The scariest part of all of the games to me were the rattlesnake-head crabs in HL2. In the first game, the thing that freaked me out the most was the moment when you're crawling through the air ducts over a room full of electrified water and head crabs... and then the duct breaks and it dumps you down into the room.
All of that being said... do go back and play Half Life if you haven't played it. I played it a couple years ago with an HD mod that increased the poly count on the character models and replaced the ingame textures with high poly versions. I heard once that they had made a Source engine remake, but that they weren't releasing it. Maybe you can find a copy of that and enjoy the updated visuals, sounds and physics that way?
