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.
YMMV: Nintendo Wars
Anti-Climax Boss: Borderline — whereas his predecessor Sturm was horribly overpowered, Von Bolt from Advance Wars: Dual Strike is barely above average at best and up against a roster full of new overpowered COs. Not to mention that the maps you battle him on are rather... pathetic, to the point where the last mission should have been called Mean To The End instead. Intelligent Systems learned from this and made doubly sure Caulder/Stolos from Days of Ruin didn't fall into the same pit trap.
Caulder from Advance Wars: Days of Ruin appears to be just an amoral scientist at first, excited by the recent apocalypse, since it finally lets him give his weapons some field testing to slake his curiosity. As the story continues, his "scientific curiosity" turns out to be genocidal sadism. He has invented a virus known as The Creeper, which makes flowers grow underneath your skin and burst through it, covering your body with roots, stems, and flowers, all of which you can feel very painfully. The original virus wasn't good enough for him since it only infected the young, so he decided to upgrade it. Now it can kill everyone, even faster and more painfully than before. The photo they show you of one of the victims of this new strain of Creeper is horrid. It gets to the point where, when he tries to Hannibal Lecture the hero about how Humans Are Bastards, the hero throws it back in his face, saying that it doesn't matter if he's right, becaue he's still a monster who needs to be destroyed. Caulder even reveals that he literally isn't human, but a clone of an amoral scientist that fought back and killed his creator and the OTHER clones of said amoral scientist. "Do you know what it's like to watch yourself die? ...It is FASCINATING!"
The same game also has Greyfield, a malicious Social Darwinist who preaches about ruling through fear. His crimes include: scaring Davis to death, messing with your units the one time he is your "ally" out of spite for disputing his darwinism, making your force do "active surveillance" for perhaps both sadistic reasons Lin mentions, murdering Forsythe before he could try being a Silent Scapegoat, and nuking his own men to kill Brenner.
Demonic Spiders: Anti-Tanks in Days of Ruinnote Doesn't help that their only real weakness after they're in position is infantry which get picked off by everything else., Pillboxes in the first Battalion Wars, Fighters and Strato Destroyers in the Battalion Wars 2.
Fandom Berserk Button: Here's a tip for being taken seriously in the Advance Wars communities: never ever suggest a sniper unit. Something about such a thing being impossible to balance right or something.
Purposefully Overpowered: The two boss COs Sturm and Caluder (Von Bolt tries to be this, but isn't quite strong enough). Nell and Hachi probably count, too.
Kanbei and Grit are often cited as being game breakers from their AW2 incarnations onwards. Although, Grit has been considered lower after DS games.
Colin also, although he doesn't fare too well against COs that get defensive boosts.
Sensei is called broken old man, for a good reason.
And if we were to toss the various Force Rank upgrades and potential tag team combinations from AWDS, we'd probably double the size of this page.
Isabella, her CO Power is, literally, Will's and Gage's combined with no drawbacks. Plus an attack boost to every unit type. This basically dominates everything. She is, to say the least, frowned upon by competitive players.
The 'Mech Rush' tactic from Advance Wars is based on this trope. In particular, Sensei's CO Powers - spawning Infantry or Mechs on every city he owns - can quickly drive opponents insane.
Colin, with his power to increase his funds by half every couple of turns on top of normal income and having cheaper units, can out Mech-Swamp even Sensei, and when partnered with Hachi or Sensei in Dual Strike, this is made even worse.
Moral Event Horizon: Waylon probably crossed it a long time beforehand, but Waylon (on Greyfield's orders) murders Forsythe execution-style, in front of just about everybody, and keeps his smug-ass attitude rolling the whole time.
The Creeper in Days of Ruin. Lin, being how she is, makes it worse by theorizing whether the infected feel the roots moving just beneath their skin.
Knowing the guy who created it, the answer is most likely yes.
Speaking of that guy, how about the extreme close up of him that shows up midway through the final mission, with him sporting an incredibly disturbing Slasher Smile? Worse, the Sound Room randomly cycles through the game's CG artwork, meaning it could show up again there when you least expect it! It's practically a Screamer.
Sea Fortress and Sinking Feeling from Black Hole Rising. Given Sea Fortress is a highly tactical mission with limited resources and an emphasis on unit placement and management, while Sinking Feeling is a highly strategic mission with a time limit and a very freeform (thus hard to Walkthrough) general strategy, it's easy to see where this comes from.
"Waylon Flies Again" in ''Days of Ruin."
Sunrise was the last mission in Days of Ruin, where you finally face Caulder. It's supposed to be frustrating and difficult... and the fact that Caulder is arguably more broken than Sturm makes it even more fun.
Greyfield Strikes from "Days of Ruin" can be very frustrating, depending on which units get sabotaged. Having landers and gunboats unusable in the first few turns will make the mission much harder and longer than it actually is.
Waylon Flies Again from "Days of Ruin" has caused some players to give up the game entirely.
Trial 7, known as Tatter River, looks like a modestly challenging trial map - 4 Commanders and plenty of Airports and Factories. But upon closer look, all of the headquarters are next to four Factories and are surrounded by rivers. Rivers can only be traversed by Infantry, Mechs, and Air Units - all of which extremely weak against Anti-Air unit attacks. Guess what the unit will be greeting you in large numbers when you try to capture a base in large numbers?
Most of the CO names in the English localizations.
Particularly Days of Ruin/Dark Conflict: Nearly every name (and themes), many missions, several units (sometimes contradicting the same unit name in earlier games) and the entirety of the script differ due to an independent European localization. The European version is closer to the original Japanese, for the better or worse.