YMMV / Sigil

• Anti-Climax Boss: The final level has the player fight Spider Mastermind and an occassional Cyberdemon, but not only are the fights done separately, but you can breeze your way through them using BFG or Plasmagun, assuming you obtained them from the previous levels.
• Fan Nickname: The evil eye decoration became known as "Sigil eye" for its iconic use as a shootable object in the wad.
• It's the Same, Now It Sucks!: While not hated per se, Sigil II certainly suffers from retreading the same ideas and design quirks from its predecessor in an attempt to replicate its success.
• Nintendo Hard: This WAD was designed to be a lot more consistently difficult than Episode 4 of Ultimate Doom ("Thy Flesh Consumed"), with frequent cramped combat scenarios, some very nasty Cyberdemon usage, and a general lack of health, ammo, and strong weaponry. While far from the hardest WAD out there, more casual Doom players jumping in on Ultra-Violence and expecting something on the level of the original two Doom games because they heard Romero made it will be in for a rude awakening. Popular "boomer shooter" youtuber Civvie 11 in his review of Sigil would even advise people to play on Hurt Me Plenty (medium) difficulty first if they weren't avid Doom players, while Gmanlives stirred up controversy within the Doom fandom when he complained that Sigil was too hard in his review... after only playing on Ultra-Violence.
• Older Than They Think: John Romero had used the lava scratch cracks on the floor and ceiling as far as in 2016 when he made the remaster of E1M8.
• Scrappy Mechanic:
  • The eye shooting switch is introduced as early as in the first level, but the way the trigger linedefs used to be placed before the version 1.2, (the first one has the switch be sealed off permanently while the other one either opens the door or raises the bridge) you could set off only the nearest one (usually the switch that raises the floor and closes the sector) by using a melee attack or missing your shot and thus render the whole level Unintentionally Unwinnable. This had since been fixed with the version 1.2 however.
  • In the sequel, some secrets can only be accessed within the first 30 seconds since the start of the level. While it's an already existing sector type in Doom engine and has been used in several custom maps, there's a reason as of why it's so uncommon, namely, that it can render obtaining 100% items and secrets impossible. And Sigil II has the misfortune of stepping on the same rake, with nary a clue as to where the secrets could be and how to obtain them within the strict time limit while having to deal with enemies at the same time.
• That One Level: E5M4: Paths of Wretchedness has a lot of player-unfriendly gimmicks thrown in by Romero himself, most infamously the crusher labyrinth with moving plates (the monster sectors are safe to stand on, but it's hard to make out at the first try) and the locked door that takes several seconds to fully open (thus stalling the player and keeping them occupied with several enemies at once).
• Visual Effects of Awesome: The level design really shows how skillful can Romero get with a more user-friendly level editor than the one he had to use back in 90's.