As others pointed out, people need to realise the mod is in a beta stage. While 3 official maps may not be a lot, these maps are of super high quality and perfectly demonstrate what the mod has to offer.
I think people who make comparisons to L4D/ZM/ZPS miss the point of this game in the first place. The way I see it, NMRiH aims for a genuinely challenging survival experience. The gameplay is as realistic as it can get without becoming annoying. Tension is delivered not by having the player attacked by overpowered super monsters, but by creating situations where the player is under stress and has to react and think quickly. None of the other games or mods that I know do that the way NMRiH does.
This is the precise strength of NMRiH. As long as it maintains its uniqueness, the player base will only grow.