Heretic (via UZDoom)

A DOOM clone with a heavy metal medieval fantasy vibe and hordes of tanky enemies—but don't worry, you have an inventory of temporary buffs, especially weapon powerups, to help you turn the tide. The problem is that, since any encounter might be the one where you actually use those powerups, the designers seem to have made every encounter with them in mind, just in case. That is, this game has maybe twice as many monsters as it needs. Most fights go on so long you're left plinking away with your wand (which takes on average half a dozen hits to kill the weakest enemies), and it just goes on and on in this seemingly-infinite march of the monsters. The best level I played, E1M5: The Citadel, is basically two conjoined medieval town arenas where you carve out territory while monsters push back—one big encounter, not many small-but-overstuffed ones.