Back in the day I got a big-box copy of Spear of Destiny and enjoyed it, though a bit less than Wolf3D. It’s levels felt too much like mazes.
I’m actually replaying SoD now too, and up to level 15 it’s not as bad as I remember. Or perhaps ECWolf’s auto-map just makes it significantly easier to navigate. Still, later levels seem to lack ammo considering the number of enemies. They appear to force the player to kite and funnel the enemies to make every shot count.
Looking back SoD does feel a lot like an expansion, since it offers nothing but art swaps and some new maps.