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.
The show as a whole has:
Ear Worm: The theme song, in all its incarnations.
Fanon Discontinuity: It's rare, but there are some fans who disregard The Black Adder due to how out of step it is with the following incarnations. A slightly more common viewpoint is that the Blackadder lineage died with Captain Blackadder at the end of Blackadder Goes Forth, and that Blackadder Back & Forth never happened.
Growing the Beard: Many fans prefer the seasons after the Re Tool. The first season has its laughs, but it's just not as much fun watching a screwball doofus and his two moron friends as it is watching a wicked snarker and his two moron friends. However, if nothing else, the first season would still be required watching purely on the strength of BRIAN BLESSED's definitively hammy performance (in fact, it's the source of the current image and caption on his page).
Incidentally, Blackadder gains a literal beard in the second season, the first one after said Re Tool.
Seasonal Rot: Inverted for the most part. The Black Adder is generally felt to be pretty average, Blackadder II awesome, Blackadder the Third a slight step down from the previous series but still very good, and Blackadder Goes Forth the best of all.
The Black Adder has:
Crazy Awesome: King Richard IV. Goes to war just for the hell of it and is implied to have killed several thousand Turks with a fruit knife.
Fridge Brilliance: Prince Ludwig permanently impersonating Queen Elizabeth nicely explains the whole virgin queen thing.
Also, Prince Ludwig is very likely an ancestor of Prince George (George IV) from Blackadder the third. George IV's great grandfather was Georg Ludwig of Germany. Which explains the uncanny resemblance (both are played by Hugh Laurie)
Growing the Beard: According to popular opinion, this is the season where it happened.
Quite literally. The original Black Adder is beardless, while the Elizabethan version is bearded, as well as more interesting, although Blackadders of the third and fourth installments are also beardless.
After the credits, we hear a tolling bell and eerie wind noises (from the intro to Elton John's "Funeral for a Friend") as the camera pans over the murdered, wide-eyed bodies of Edmund, Percy, Queenie, Nursie, Baldrick, and Melchett. We then see Queenie there, alive and well, before she turns to the camera, gives a chuckle in a strange voice and says, in the master of disguise Prince Ludwig's voice, "Now this is a disguise I'm really going to enjoy. If I could just get the voice right." A CREEPY end to the season.
Blackadder: You mean they actually rehearse? I thought they just got drunk, stuck on a silly hat and trusted to luck.
Blackadder: Well, you could appoint him a high court judge.
George: Is he qualified?
Blackadder: He's a violent, bigoted, mindless old fool.
George: Sounds a bit overqualified!
Anyone else who isn't Edmund Blackadder.
Cargo Ship: Lord Sod-off Baldrick has a relationship with his turnip.
Crowning Moment of Funny: Blackadder in "Dual and Duality": "A man may fight for many things: his country, his principles, his friends, the glistening tear on the cheek of a golden child... But personally, I'd mud-wrestle my own mother for a ton of cash, an amusing clock and a sack of French porn."
Hilarious in Hindsight: The ending of "Nob and Nobility" has Baldrick elevated to being a lord over Blackadder, much to the latter's annoyance. In 2013, Baldrick's actor Tony Robinson was knighted, while Rowan Atkinson "only" got a CBE.
Lawful Evil: Although Edmund claims that his only loyalty is towards himself and that he is incredibly ruthless and cold, only the latter is completely true as he demonstrates a great deal of loyalty for his boss, despite the fact that his boss is incredibly stupid and that he (Blackadder) could manipulate him into giving up all of his (The Prince) money and power to him. He even risks his own life for him. But abandons The Prince after he is mortally wounded. Making him a Type III Lawful Evil character.
Magnificent Bastard: This series's Blackadder is a prime example, certainly the most outright evil and manipulative of the dynasty. The only one who not only doesn't die at the end of his series, but actually achieves his goals. The one in Blackadder: Back & Forth does too, admittedly, but he had a time machine - Blackadder the Third's Blackadder did it with just his cunning and wit.
Blackadder Goes Forth has:
Awesome Ego: Lord Flashheart could potentially be the poster boy of this trope.
Blackadder: Yes, why not? When this madness is finished, perhaps we could go cycling together. Take a trip to the Old Swan at Henley and go for a walk in the woods.
Given that nowadays there's a heightened awareness of hate crimes, Flash shooting the Red Baron in cold blood and then yelling a homophobic insult at his corpse is pretty awkward to watch. Not that it wasn't in character.
The line "Cancel the state funeral, tell the King to stop blubbing, Flash is NOT DEAD!" may be a bit more difficult to laugh at now that Rik Mayall, who played Lord Flashheart, has passed away.
Ho Yay: "Baldrick, I love you. I want to kiss your cherry lips and nibble at your shell-like ears."
Older Than They Think: Much of the anti-war themes, tropes, and character archetypes relating to World War I (or the Great War, if you prefer) are present in the British war comic series written by Pat Mills and drawn by Joe Colquhoun, "Charley's War."
Tear Jerker: Highly unusual for a comedy series, but the last episode of Blackadder Goes Forth cannot fail to bring tears to anyone's eyes.
It aired on Remembrance Sunday with no complaints. Such is its power.
It's made all the more heartrending in the audio only version, where, since you can't see them, you have to imagine them going over the top, and as the sad reprise of the main theme is happening, you can hear a line each uttered by a character earlier in the episode; George: "We've had some good times, we've had some damn lovely good laughs.", Baldrick: "I thought it was going to be such fun, too.", Darling: "But sir, I don't want to...", and Blackadder himself: "Good luck, everyone...".