Bandos gets a moment of awesome in possessing Zanik for the first time to kill Sigmund.
It becomes more awesome in hindsight when a tier list was made to show the power of each god. Bandos was up in the tier with Saradomin and Zamorak, two of the key gods in Gielinor's lore, before getting dropped into the next one due to the player's interference. It wasn't just screwing over Bandos' plans, but severely weakening him as well.
Guthix versus Bandos in the backstory. Sure, there was pretty much no way that a transcendent being like Guthix could ever lose a fair fight to a lower tier god. But Guthix's Kirk Summation to Bandos and declaration that the creatures Bandos brought to Gielinor were to be freed of Bandos's tyranny, and the casual way Guthix knocked Bandos back to Yubiusk definitely qualify as awesome.
The end of the Legends Quest. For reference, the player just defeated Nezikchened, a powerful demon who put a curse on the Kharazi Jungle. Nezikchened swears that he will return, more powerful than ever. Your response?
Although it happens after Guthix's death, watching Saradominfail to teleport you, demonstrating your new anti-god ability was very awesome at the end of The World Wakes.
More impressive in that the teleportation spell flawlessly whisked Nex, Char, and several renewed strong Mahjarrat. Saradomin has good reason to be surprised.
Also, the player, should they chose to do so, manages to motivate the Guardians of Guthix to fight against what seem to be impossible odds.
When players first logged on after the RuneScape 3 update, they were met with a cutscene showing Zamorak and Saradomin meeting outside Lumbridge, and engaging in a Beam-O-War. It caused the area between Lumbridge and Draynor to turn into a blasted battleground, with glowing green rocks everywhere. This was the setup for the first World Event; players can choose to fight for Saradomin or Zamorak, gathering as many of the green rocks, or "Divine Tears" as possible to empower their chosen god and help them overpower the other.
Now we know why Tumeken, the Menaphite sun god and head of that particular pantheon, hasn't shown up in the Sixth Age. Back in the Second Age, when the Mahjarrat joined Zaros, there were about 500 of them. Tumeken reacted by suicide bombing an entire race of Humanoid Abominations and wiping most of them out. The downside to this was that the land they were in became a desert, and about half of Tumeken's people died with him.
The Mighty Falls is one for both General Graardor and the player. Graardor picks up a weapon for this fight, and he goes from being easily the weakest of the God Wars Dungeon bosses to a truly terrifying foe. He smashes the arena throughout the fight, forcing the player to literally fight him up close the entire time, two or three swings of his kyzaj can end the player if they strike, and he is far more durable to boot. To compensate, the player uses a completely foreign weapon for the first time, and manages to win. Earlier on, the player is able to defeat the troll champion without any armor, which in the Evolution of Combat, means a much smaller lifebar.
To add to this the three fights in the Kyzaj Tournament, Yelps the goblin, who used his wealth to buy lucky Bandos gear such as a Godsword, armor and bodyguards and gets beaten by the player; Lol the troll, who you fight with no armor, and still beat; and Graardor, who fights like mentioned previously.
Furthermore, at the end of the Graardor fight, the rules of the tournament say that the loser becomes the winner's lieutenant in the army; meaning Graardor now answers to Zanik. The bandosians respond by bringing Zanik into the arena and forcing you to kill her to prove you are a worthy warrior; but you can choose not to. The result of sparing her is that se becomes the leader of all Bandosians and resolves to move them to their home plane of Yu-bi'usk.
Plague's End, the finale of the elf quest series, wrapped up not only the longest, but one of the oldest quest lines in Runescape, which covered a large amount of content. All of the loose ends were tied up, resulting in a continuous awesome moment. Some highlights:
Remember back when this quest was about a plague and some annoyingly inefficient public officials? The writers of the quest sure do, and they resolve the fate of the people of West Ardougne in the most satisfying way: revolution. The player breaks the truth of the plague and the Death Guard to the people, and they storm the Mourner Headquarters along with all of the NP Cs from the early quests and kill the Mourners.
King Lathas, who has been collaborating with the Mourners and Lord Iorwerth, sends troops to retake West Ardougne. The player was ready, though. Members of the Ardougne City Council note Ardougne appears to have a constitutional, rather than absolute, monarchy were already alerted to Lathas's doing, and had issued an order for the city militia to stand down. The Knights of Ardougne and the Heroes' Guild members side with the Council, and King Lathas is overthrown.
The Tyras troops get their own awesome moment. By timing their last stand against Iorwerth to coincide with the player rebuilding the elf city of Priffdinas, they prevent him from sending troops to stop the player and the elders.
An honourable mention goes to the elven elders themselves, and how they hid from Lord Iorwerth. One turned himself into a tree. Another hid in the spirit plane. One of them hid on the other side of the main continent in a hidden dungeon that could only be accessed using her potion recipe. One of them died, but still made sure that her wisdom could be passed on to any clan member who could see a statue of her greatest work.