These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Deader Than Disco: Despite being one of Marvel's top books in the 1970s, the title's disastrous "New Defenders" revamp, the resurgence of the X-Men as a popular franchise, the rise of various spin-off books (New Mutants, X-Factor, West Coast Avengers), and Marvel moving the founding Defenders back to being solo heroes (and Namor being absorbed into the Avengers franchise), the book fell into a state of mockery as far as as a relic of a past period and not fit for modern comic readers. Attempts by Marvel to revive the book has largely failed and the only real successful revamp was a mini-series by the guys behind Justice League International which basically reduced the concept to an "odd couple" comedy. The Marvel NOW! version, Fearless Defenders has its work cut out for it.
Fanon Discontinuity: All Elf With A Gun appearances that were not written by Steve Gerber, including the pay-off to the whole thing where it was revealed that the Elf was killing off nexus people who were a threat to the stability of the timeline and that the elf was part of a larger group of elves that were trying to stave off an apocalypse that would occur if the founding four Defenders stayed together.
Hilarious in Hindsight: At one point the team had Daimon Hellstrom, the Son of Satan, as a member at the same time as Devil-Slayer.
Bendis's controversial revamp of the Avengers has been denounced as him basically taking the Avengers and turning it into the Defenders. This was acknowledged by Bendis himself several years into his run, when he had Nighthawk say "Clearly you guys are the Defenders," during a period when the team consisted of Wolverine, the Thing, Luke Cage, Jessica Jones, Doctor Strange, Mockingbird, Ms. Marvel, and Squirrel Girl.