I can think of a handful of games that, despite being games that I’ve enjoyed, never really became part of a “genre”. Do you have any like this, and if so, which?
Are they games that you’d like to see another entrant to the genre to? Would you recommend the original game as one to keep playing?
Project Zomboid is very similar thematically to Cataclysm (zombie apocalypse, loot world for supplies to stay alive), but is far simpler in every respect, is real-time rather than turn-based, plays on handcrafted rather than procedurally-generated maps, has its zombie infections be incurable, and has combat that I really don’t like (though Project Zomboid also has a much gentler learning curve and a loveable raccoon mascot). I’m not sure if one could reasonably put it into the same genre. Maybe.
It’s important to note that Project Zomboid uses partial procedural generation, primarily to handle building interior furniture and loot spawning.