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.
It turns out the Nod fans were right, the conclusion of 4 states that all Nod members vanished from Earth after he activated Threshold 19.
By the end of Tiberian Twilight, Kane is revealed as having more-or-less made many things up as he went along. In the first two games, he tried to take over the world. In the third his main purpose was to gain the Tacitus and the Scrin Threshold. In the last game, having seen (twice) that fighting GDI is futile, he allies with them, because what he really needed all along was access to the resources to build a power source for the Tower (the TCN) and a key to unlock it (the Tacitus). Supposedly, after having conquered the world in either of the first two games, he intended to bring the Scrin to Earth, steal a Tower, build a TCN and Ascend... which is, you know, precisely what happened in the end.
Broken Base: There's always been contention over whether the games made since EA acquired Westwood were any good, though both factions have come together to decry Tiberian Twilight.
Draco in Leather Pants: Even before Nod was humanized in the last two games, they had a following seeing them as benevolent freedom fighters and at worst, seemed to pretend that Nod's numerous acts of evil didn't even happen or actively believing them when they blame their own atrocities on GDI.
Fan Nickname: The venerable Mammoth Tank is a "Mammy," while the boxy subterranean Flame Tank from Tiberian Sun is the "BURROWING SHOEBOX OF HORRIBLE BURNING DEATH."
Fanon Dis Continuity: Fans still debate a number of issues, notably which ending of the first Red Alert leads to Tiberian Dawn, or whether even it makes sense to include Red Alert 1 in the Tiberium continuity at all.
In addition, most fans consider most (if not all) of the Tiberium Wars novelization non-canon.
Game Breaker: Mammoth Tanks, the Commando & Transport Chopper combo, Tiberian Sun's Artillery and Subterranean APCs, Rocket Launchers...
Tiberian Sun's Artillery is especially bad, mostly because of how accurate they are against moving targets. Even the strongest armored units in the game, including the Mammoth Mk.2, will be torn to pieces by just a few Artillery. They effectively obsolete the Obelisk of Light in terms of ground defense, since in addition to greater range and lower price, they require no power and will pulverize groups of infantry, unlike the Obelisk. For balance purposes, they were nerfed in Firestorm.
The Black Hand; the original infantry was already nigh-unstoppable, and there's an entire faction dedicated to them, which lets them completely destroy everything on the ground, adds other units such as the best Anti-Air in the game, the ability to add a Black Hand to all your base infantry squads, a Humongous Mecha based on the avatar that has a flamethrower which can fire while it's moving, letting a group raze entire bases just by walking by, There's also the fact that a single Black Hand squad can defeat a Sniper Squad, despite the fact that A: a Sniper Team is a dedicated anti-infantry unit while a Black Hand Squad is an anti-infantry/anti-building unit and B: The Black Hand is in fact, cheaper than the Sniper Team.
The MARV from Kane's Wrath is a giant tank that can garrison four infantry, fires sonic waves from a three-barreled cannon, can instantly harvest Tiberium, and with the right combination of infantry is nigh unstoppable.
Hell Is That Noise: If you're up against a Nod force, the Obelisk of Light's charge-up hum.
Hilarious in Hindsight: In Tiberian Dawn, Seth is executed by Kane for trying to order the player's forces into making a full frontal attack on the Pentagon. In Tiberium Wars, the second GDI mission has you defending the Pentagon from a full frontal attack by Nod forces.
Love to Hate: Kane is one of the most well known PC game examples.
The Cyborg Reaper from Firestorm travels on four insect-like legs and attacks by trapping infantry in a net and proceeding to pummel them to death with missiles. Comes complete with a creepy computer voice and a skull like face.
Everything to do with Cabal's army. It's outright stated that after he took out Nod high command, he started harvesting soldiers and civilians alike, from both sides, to be converted into his cyborg army. In the GDI mission you have to destroy one such processing facility, where the civilians and soldiers are herded into camps like cattle, before being pushed through what looks like an assembly line, pooping out a cyborg at the end. Technical limitations negated some of the horror (as the humans just sort of drop dead when they enter the "converter" and a Cyborg takes it's place) but still terrifying nonetheless.
The Nod ending in Tiberian Sun. McNeil is captured and has obviously suffered torture, the Philadelphia is destroyed by Nod's ICBMs (and Slavik forces McNeil to watch it!), and Kain launches his world-altering missile, turning Earth into a Tiberian wasteland.
Ron the Death Eater: GDI gets this big time for being Nod's main enemy, with many fans arguing GDI are the real villains, ignoring things like they are the ones who frequently have the missions to defend civilians from Nod, and in Tiberium Wars, the Scrin, while Nod's mission frequently having them carrying out massacres and during the Scrin invasion not lifting a finger to stop them.
Rooting for the Empire: Nod has a lot of fandom support, with the closest thing GDI has likely gotten to having any is the criticism that Kane's Wrath only had a campaign for Nod (though the Scrin not having one either was also criticized).
Villain Decay: Kane. The later games in the series make it questionable if he even is a villain... and his obviously evil actions in previous games backfire on him several times.
The Woobie: The Forgotten. The amount of hell they suffer through in Tiberian Sun and Firestorm must take some form of record. In the end they just give up on the rest of the world and go to the Red Zones where no one would follow.