Who told you that this is a horror game? The official description is "7 Days to Die is an open-world game that is a unique combination of first-person shooter, survival horror, tower defense, and role-playing games."
Erm you just said it yourself "Survival horror" As for the tower defense part, i'd say not really. You want a zombie game with actual tower defense? play Night of the Dead, it has nightly zombie hordes by default. Also has proper traps for a tower defense game which 7dtd sorely lacks to fit the genre. Not only that but with the new ai and how exploitable it is, its not really tower defense, its force them into killbox to get mowed down while they don't damage the base at all otherwise. It USED to be tower defense back in a16.4 as blood moon zombies came from random sides each wave, and you could not herd them into a specific spot, you had to defend all sides. As for its role playing parts it also does that very poorly, with a poorly thought out skill system. Just because you have a rpg like skill system does not make it a rpg, you need story and an actual plot.
I've seen mods with actual story Age of Oblivion to name one, it has a actual story with boss fights and custom boss poi's and its all made by 1 person by themselves. Has lots of custom enemies and gear too.
7dtd is honestly pretty much garbage in vanilla without mods in todays version, its just not any fun anymore best time i've had with vanilla was 16.4 as that was the best skill system its ever had and its just gone downhill since.
Some stuff the game needs:
Better natural feeling progression instead of this forced stuff the game has now, you want us to go to other biomes? give us a reason to, make each biome have a special material that only drops there and is used to make special gear related to that biome that is better than the generic iron/steel stuff. Most survival games do this. You want better gear? you need to go to harder biomes to upgrade and craft it. Also remove the town size limitations, and restore the randomized traders back. You can set it so 1 of each proper trader is forced to spawn in its proper biome while every other spawn is randomized.
Bigger inventory size, I'm sorry but with how slow vehicles are and how tiny the player inventory is it needs a drastic size increase, I'd say maybe add at least 15 more slots, I use a mod that ups it from vanilla size to 60 slots, and it just feels right, its still easy to fill it and have to toss things, but the extra 15 slots is some real quality of life.
Better zombie progression, the hp jumps between normal to ferals to radiated is kinda too big of a sudden jump. Could use some in between tiers. maybe 1 between normal and ferals, and 2 between ferals and full radiated.
More items and progression of those items. Steel has been the top tier material for well, a very long time, I been around from as far back as 10.2 and always remember steel and radiated enemies being the top tier and then nothing else, we need stuff above that. We also need more guns, don't need more ammo types, but we need more varied guns than the game has. We also need weapons to have a balance pass, as many of them just do far to little damage for being guns.