I’d argue the entire game is the boss intro. And IIRC, the lore behind Gwyn is pretty deep too. You fight all these big baddies, and when you get to Gwyn, he’s relatively pretty weak.

I remember being very fascinated by all the dark souls lore and his was particularly interesting. I vaguely remember that after killing him, you have the choice of keeping the flame alive or leaving and breaking the cycle?