Bloodlines was a game that, when I hit a game stopping bug at the end game that prevented me from completing the game, I swore at the game, and immediately restarted from the beginning and didn't care.
I played through the game several times before mod support even existed.
Bloodlines isn't a classic because the mod community gave it new life. Bloodlines had a mod community because the people that enjoyed that type of game fell in love with it.
In spite of getting a blocking bug (that likely just needed a restart of the level, not the whole game), I still played and loved the game.