The beginning of Wei's story in 8, Escape from Luo Yang: Cao Cao has failed to assassinate the tyrannical Dong Zhuo and is captured. It's almost certain that he'll be executed for treason. So, will he give in to the predicament? Hell no! He steals one of his captors' spear and throws it at Dong Zhuo to distract Lu Bu who predictably blocks the spear away from his tyrannical lord. While Lu Bu is distracted, Cao Cao uses that chance to get the hell out of there to Xiahou Dun and Xiahou Yuan who was waiting outside. Both retainers anticipated their lord's failure and found he's being chased by Dong Zhuo's men. Xiahou Yuan shot arrows to their chasers and Xiahou Dun gives Cao Cao his sword. Then, three of them began their running from Luo Yang. In addition, Lu Bu is available as Bonus Boss. That's right, you get a chance to face Lu Bu in the very first stage of story mode, unlike the usual where you wouldn't face him until Hulao Gate! As if Wei needs more proof to emphasize their badassery!
What's even better about it is how it shows Cao Cao in its lowest state and from certain point of view, he is basically a nobody. Now compare his state as story progresses where he becomes a nightmare (for his enemies, anyway) and essentially the most powerful man in China. Also, unlike Wu and Jin, Cao Cao and his Xiahou cousins have nothing but their pride, strength, and small group of loyal soldiers in the beginning of their story. At least Wu and Jin begin their story mode where they're already an established faction. Now more Fridge Brilliance kicks in when you realize Liu Bei and his brothers also doesn't have any homeland of their own for the majority of the first half of Shu's story mode, and how hard they had to struggle to realize their dreams of benevolence. In the end, Cao Cao and Liu Bei are not so different, after all.
Four words: The Battle Of Chibi/Red Cliff. 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/the book/the whole of Chinese history, 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.
The Battle of Heifei is one for both Wei and Wu. Wei for being able to turn the seemingly unwinnable situation and defeat the Wu army, and Wu being able to escape with only limited casualties, despite having to face The Dreaded Zhang Liao. This gets further explored in 8 where Wei was able to pull this off despite Li Dian and Yue Jin not agreeing with Zhang Liao, putting aside their differences and being able to improvise a devastating pincer attack. And on the other side, Ling Tong and Gan Ning finally putting aside their differences to protect Sun Quan and take some Wei officers down. Both sides ended up forming True Companions from this battle.
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 Jin, convincing Xiahou Ba to stay, keeping Guo Huai alive, turn Wen Yang to your side and "fixing" Zhuge Dan will allow you to counter Wen Qin's ambush and save Sima Shi. However, the real fun begins with the next two obligatory stages. They have Sima Shi conquering Shu and then Sima Zhao conquering Wu right after, uniting the land in a relatively short period of 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!
In Dynasty Warriors 8: Xtreme Legends, Wei's seventh alternate if stage features a revised Battle of Mai Cheng, with Wei facing Wu and Shu. The allied forces receive reinforcements from Shu in the form of Huang Zhong, Zhang Fei, Ma Chao and Zhao Yun. On Wei's side, Zhang Liao and Yue Jin arrive from Hefei. This actually means a full confrontation between Shu's Five Tiger Generals and the Five Generals of Wei.
Each of 8's final hypothetical battles may also count:
Wei's final battle has the perfect climax to how Cao Cao would fight Liu Bei. With the eastern half of the country in his control, Liu Bei surprisingly takes control of Liang, Hanzhong and Yizhou, essentially making the western half of the country. The entire battle, even with Zhuge Liang's schemes is a complete massacre on Liu Bei's side, all without Sima Yi's presence. Even when killing his rival, Cao Cao chooses to uphold Liu's wish of making a land for the people.
Shu ends with a final assault on Xu Chang. After decades of running from Cao Cao, Liu Bei finally has the upper hand, and with all his supporters, they completely outperform and outsmart Cao's troops. When Cao Cao receives the final blow, he reminds Liu Bei of the evil in the hearts of men, but Liu Bei replies that though Cao is right, the good of the heart should still be believed in, and Cao Cao's final words, to try it out, seals the deal between the two.
Wu's ending has them take out and dismantle Xu Chang, but unlike the other kingdoms, they don't actually slay any of the officers, and all of them end up retreating as well. After yet another fire attack to the castle's throne room, Cao Cao is confronted by the entire Sun family, and Sun Quan gives the proposition that all three of them, himself, Liu Bei and Cao Cao just rule the entire country together. Cao Cao flat out rejects the offer, knowing that his path of ambition needed to end for peace. In the end, the China is being ruled, by all three kingdoms.
Jin has the Sima clan conquer both Wu and Shu, with a notable lack of hostility to the Cao clan. Jiang Wei once again proves his stubbornness by assembling himself with Wu's remnants, joining together in the area that cost Cao Cao's ambition, Chi Bi. Even against a fire attack, the Sima clan continue to push through, showing the difference between then and now, and eventually defeat Jiang Wei. What happens when Jiang swears to turn into a ghost in the afterlife to oppose the Sima clan? Sima Yi, Shi and Zhao all shouting "Imbecile".