Four words: The Battle Of Chibi. The combined (yet still massively outnumbered) armies of Shu (led by Zhuge Liang) and Wu (led by Zhou Yu) against the MASSIVE naval fleet of Cao Cao's Wei. ALWAYS one of the absolute most important battles in any installment of the series, and one involving ridiculous amounts of badassery from all three sides.
Wei gets at least three:
The first one is when Xiahou Dun gets his eye shot out, rips the arrow out, and proceeds to continue the fight! Unfortunately, his eyepatch is applied immediately after the cutscene, and there's no indication of the rumor that he ate the eyeball.
In the cutscene after that same battle, Zhang Liao basically telling Lu Bu to stop being a pussy and accept death like a man — which is implied to be the reason that Cao Cao chose for Zhang Liao to live and Lu Bu to die.
Dian Wei's death counts as both awesome and a bit of a Tearjerker
Huang Gai setting the Wei ships ablaze is pretty damn awesome.
If a cutscene must be a crowning moment of awesome, then Jin's ending is the best way to end the game.
Even moreso, that cutscene takes the usual 'Liu Shan not grieving on Shu' scene and have Liu Shan make a good statement about people shouldn't be too bound on past tradition to achieve peace, a statement that Sima Zhao agreed on... and in turn... makes the grieving Shu officers cheer in joy and probably makes an in-universe Rescued from the Scrappy Heap for Liu Shan.
The battle of Chang Ban for both Zhao Yun and Zhang Fei, the former for single handedly saving Liu Bei's infant son and the latter for pulling a You Shall Not Pass and to make his point he roars at them scaring the crap of most of them.
Dynasty Warriors 7: Empires has a Skirmish mission where you get to drive a juggernaut. Sure, it's slow, but it's close to invincible, and pressing Circle shoots out jets of flame in a 270-degree circle around you. Drive it into a thick crowd of enemies, park flush against a wall facing it, and just press Circle every four seconds or so, maniacal laughter optional.
Dynasty Warriors 8: Battle against Yu/Gan Ji. There's just something awesome seeing Da Qiao, who's mostly presented as the meek Reluctant Warrior, getting enraged and readily throws herself to kick phantom soldiers' asses and Yu Ji himself because he messed with her husband. What makes this awesome is that Da Qiao has never done this in the previous games even if Yu Ji has been a recurring NPC since 4XL, this is the first time we see a pissed-off Da Qiao.
Zhang Bao, Jiang Wei, and Ma Dai's Big Damn Heroes moment when they rescue an isolated Guan Xing at Luoyang.
Sucessfully enter any "What If" path in Dynasty Warriors 8.
For Wei, the very fact of winning at Chibi with the help of a not-dead Guo Jia and a convinced Xu Shu. It mainly involves catching Pang Tong and unlinking the one ship Huang Gai targeted for the fire attack so it doesn't spread on the other ships.
For Wu, averting the deaths of everyone playable who would have died up to Hefei leads you to ambush Zhang Liao before he could destroy the bridge and thus, winning handily the battle of Hefei.
For Shu, by meeting again with Xu Shu at Chibi and denying Pang Tong's death, you can deny the flood attack at Fan Castle and mop the combined forces of Wu and Wei, averting Guan Yu's death at the same time.
For Lu Bu's force in Xtreme Legends, saving the lives of Hua Xiong and Wang Yun as well as gaining the gratitude of Yuan Shao for saving him several times leads to Hua Xiong making himself a decoy (doing what you were supposed to do in the historical road) as well as gaining reinforcements from Yuan Shao and Liu Bei (the latter being asked by Diaochan), averting the defeat at Dingtao.
What, no mention of Lu Bu? Every time you meet him is a moment of awesome. He comes with his own theme music, for crying out loud!
And let's not forget being able to play as him. Especially in Dynasty Warriors 6, where the final level in his story line is basically Lu Bu and his handful of followers against all Three Kingdoms, Yuan Shao, Dong Zhuo, and Zhang Jiao, with the last two coming back from the dead just to fight him! If that isn't a CMOA, I don't know what is.
There is an equivalent in the form of Dynasty Warriors 8: Xtreme Legends' Final Hypothetical Stage for Lu Bu's forces where All Three Kingdoms and Yuan Shao combine forces to protect the emperor from Lu Bu's own ludicrous might. While it doesn't ressurect Dong Zhuo and Zhang Jiao, this still equals over 60 officers, including over 20 playables against Lu Bu, 3 other playables and a handful of generics. Everyone on the other side dies.
And sealing the deal is the Hypothetical Ending as well. Lu Bu deposes the emperor, but that's after revealing his honest intention: He wanted to ensure that there's no corrupt people running around China (eg: The Eunuchs, Dong Zhuo) and for that, absolute strength is required and he's the man for the job, the Emperor is just too weak to keep them in place. Thus Lu Bu becomes an Emperor of China through power, and he's even cheered for it. For all things, it was pretty awesome to show that beneath his Chronic Backstabbing Disorder lies a Noble Demon that just wants peace in the land.
There's also the act of beating Lu Bu at Hu Luo Gate, at the point where he's at his strongest, Especially on a higher difficulty when everyone in the Allied forces it telling you avoid the guy like the plague. Lower level, you've overcome the odds and beaten him. Higher level, you've come very far and outshone China's greatest warrior. I challenge you to beat the guy on Harder Than Hard and not feel like a badass!