* CreatorBacklash:
** Adrian Carmack apparently detested working on these games. He even placed four hanged Commander Keens in the second secret level of ''VideoGame/DoomII: Hell on Earth'', that you have to gib in order to beat the level, as revenge for having to work on a LighterAndSofter video game series.
** Tom Hall has flat-out stated that he despises the 2001 GBC game, and doesn't even count it as being part of the series. He also considers ''Keen Dreams'' to be the "lamest" of the ''Commander Keen'' games. He was definitely not too excited about the (eventually cancelled) mobile game, either, stating [[https://mobile.twitter.com/ThatTomHall/status/1137907336750567424 it didn't feel like a Keen game.]]
* EasterEgg:
** In one level of episode 5, some pipework forms a swastika (a reference to the then-forthcoming ''VideoGame/Wolfenstein3D'', although the swastika is actually the mirror-image of a Nazi swastika) and other pipework below it spells out the name of Creator/JohnRomero. In another level, pipework spells out the name of TomHall.
** A secret reference that wasn't found for 25 years was revealed by Tom Hall on Twitter: Keen's [=CompuWrist=] is a modified Platform/AtariLynx. The letters of the logo can ''just'' be seen, scratched out on the top, with the Atari logo scratched out at the bottom of the screen.
* FranchiseKiller: While id Software was already becoming less and less interested in making ''Commander Keen'' games, especially after Tom Hall left the company in August 1993, many believe that the 2001 GBC game (with its poor sales and mixed reception) was the final nail in the coffin for the series. The announcement of the mobile ''Commander Keen'' game, eighteen years later, aimed to revert this, but it was quietly cancelled a year later after mostly negative reception.
* KeepCirculatingTheTapes: The full version of the sixth game, ''Commander Keen in Aliens Ate My Babysitter!''. It's the only game not on ''Platform/{{Steam}}'', where you can otherwise get the full series (including the GaidenGame). This is because the sixth game was published by another company which has since gone under. ID was approched by [=FormGen=] to put out a retail title and decided to give them episode 6 and make it stand alone from the ''Goodbye Galaxy'' series, making it a two episode series where Apogee usually sold titles in sets of three.
* OrphanedSeries: Although these games are a fairly enjoyable way to spend an afternoon if you're not busy, they were discontinued before a satisfactory conclusion could be reached, and a number of copyright hand-changes have made an official conclusion more or less defunct.
* ScrewedByTheLawyers: The sixth episode of the series, ''Aliens Ate My Babysitter!'', has never had a modern rerelease due to the game’s publisher [=FormGen=] going defunct and the rights to the game being uncertain. For several years, ''Keen Dreams'' was also in a state of limbo due to not being owned by Apogee before finally getting licensed and rereleased in 2013.
* {{Vaporware}}: Despite having an animated trailer, the mobile game announced in 2019 appears to have been canceled in 2020. A Google Play Store listing for it exists, suggesting it at least made it to beta testing. The game is not available to download there though, and the reviews from people who actually DID play it were unanimously negative.
* WhatCouldHaveBeen:
** id tried to publish the first game through Softdisk, as they already had a contract with them. Softdisk rejected it because the game didn't work with CGA, but they did later publish ''Keen Dreams''. The game also started life as a port of ''VideoGame/SuperMarioBros3'', but Nintendo wasn't interested in MS-DOS games [[note]]Nintendo were impressed by what id had done but had already made the decision to focus on their own console. Both Nintendo and Creator/JohnCarmack have acknowledged this was the right decision.[[/note]] so id kept the game engine while creating their own content.
** John Carmack once stated on Twitter that he had plans to develop a ''Commander Keen'' game for [=iOS=] devices, but nothing ever came of it before he left id Software. The QuietlyCancelled 2019 mobile game was made without him.
** Carmack had once expressed interest in personally working on the Game Boy version with Romero and Tom Hall contributing to level design.
** A mobile game by Creator/BethesdaSoftworks was announced at E3 in 2019. The game would have taken place years after the original games, and focused on Billy's twin son and daughter, Billy Jr. and Billie. The numerous gameplay changes and pay-to-play nature were roundly eviscerated, and it was unceremoniously cancelled in June 2020, with Bethesda scrubbing practically every trace of it from their websites.
* WritingAroundTrademarks: The game originally started as a ''VideoGame/SuperMarioBros3'' clone for [=PCs=]. id tried to get Nintendo to distribute it, but they weren't interested, so they used the engine to create an original game.