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.
Check the game files for Upbeat 3.ogg. It's the best of the battle music in the game, and it's quite awesome.
Pretty much the entire score counts as Crowning Music of Awesome, and that's what makes the game so addictive, at least to this troper; the music draws the player in and doesn't let go.
Fanon: This stunning piece of fan-lore that builds upon and extrapolates the game's canon to explore the culture and history of the Sins factions in more depth. Though for some reason the two pages of the thread are the wrong way round.
Game Breaker: Carriers before the last few patches. Most battles were decided by who had the most carriers and thus the most fighters. Not even dedicated anti-fighter ships could stop the fighter spam from a few carriers!
In the Expansion Rebellion, the Vasari Rebel Kultorask Titan has Nano Leech which drains both hull and antimatter to restore itself. Leveled up, the Kultorask can sustain an infinite amount of hull and antimatter from large fleets and destroy virtually any sized enemy fleet.
This is nothing compared to the Vasari Rebel Orkulus starbase though. Stronger than a level one Titan, the ability to phase jump to any gravity well, and function as a phase stabiliser anywhere, four or more Orkulus starbases can summon entire fleets anywhere in the game. When combined with a Kultorask Titan, a single Rebel Orkulus starbase can be nearly invincible.
Scrappy Mechanic: The Open Rebellion event for Stellar Phenomena. If allegiance drops to less than 30% on planets, a sizable fleet of rebels, complete with their own Capital Ships, will attack the planet, destroy everything they can, and automatically destroy the colony. Since planets more than 5 phase lanes away have a maximum of 35% loyalty, and Deliverance Engine signals guarantee at least a 10% drop, playing against an Advent player is an exercise in futility as the colonies are overthrown faster than you can restore them. Not even TEC Rebels, who are "assaulted" by fleets of non-combative forces, are still prone to this.
This has been made somewhat hilarious by the presence of an actual LotGH mod.
Stop Helping Me!: The various superweapon buildings your allies can purchase are one of your worst enemies. Every time you conquer an enemy planet, a nuke your allies shot at it 20 minutes ago will finally arrive.
What's worse than having a planet you conquered blasted by a superweapon that was late to the party? Having your allies colonize it before you can, even if you did most of the fighting. However, if they just happened to fire a Novalith or Kostura beforehand, it can instantly turn into a Crowning Moment of Funny.
Unfortunate Implications: The Advent's racial telepathic bond called "the Unity" MIGHT be a form of mass brainwashing. But since the lore is a bit fuzzy here this might just be a proto hivemind.