When I played through Heretic a while back, I did play the original campaign and the expansion. It did feel a bit repetitive by the end. Still the art, interesting levels, and coherent–if sparse–story made it worthwhile for me.
Also the MP is fun, even if it sometimes feels too much like a Doom reskin. I wish they had at least made the weapons all projectile based, since hitscan feels especially out of place given the fantasy setting. Perhaps they were concerned with lag from too many projectiles, as things like DWANGO served low-bandwidth dial-up connections.
