I figured, to make it more 'official', I'd compare Left 4 Dead's Finale encounters (instead of all the infected themselves) versus the Patriach, because that is essentially what both are, the Final Boss.
The 'Finale' is a special case where the Survivors, in order to be rescued, have to make a TON of noise, attracting enough infected to create a really nuts 'last stand'. Whether it be generators, a rock concert, a bombing run, or simply radioing for help (Left 4 Dead's finales were a tad flimsy, eh?), this usually attracted everything to you while you either held out or did simple tasks. Usually the finales are split between Horde Wave > Tank >Horde Waves > Tank > Mad Dash to Rescue Craft as Everything Comes After You. Sadly formulaic but still one hell of a thing to live through.
On the other hand...
Kevin Clamely, the Patriarch's original identity, was the CEO and founder of Horzine Biotech, the company responsible for the outbreak in London. He was hired by the government to create the perfect soldier—something that wouldn't experience pain or fear, and wouldn't question or reason. London was to be used as a staging ground—a test of Horzine's accomplishments. Kevin thought of the clones as his "children" and "family" because they were the only companions he had left.
Sergeant Masterson was Horzine's last project before the outbreak. He escaped from the Biotics Labs below the city through the sewer system to the city above, hoping that he could rebel against his mad creators. Sadly, this is what Kevin wanted all along; Masterson led his soldiers into combat, and they were killed just as Kevin had planned. With the British Disaster Response Force eliminated, nobody could stand in the way of the clones.
Horzine's methods were deemed too immoral even for such a controversial project, and were shut down. However, the project didn't want to be shut down. In a second complex deep underneath the city of London, the experiments continued.
Eventually, he realized that his work was in jeopardy. His scientists were leaving and he feared that someone may reveal his secret work to a world that wouldn't understand or even allow it. In a final act to save his dream, he asked the remaining scientists to take the most advance pieces of technology at their disposal, and use the methods they had perfected over the course of their work to implant them into him:
* An updated version of the cloaking device used on project Stalker
* Three modified neuro-stimulation systems similar to those used on project Guardian
* A nerve-controlled weapons platform on his left arm.
Finally, he underwent the same "gene-enhancing" process that all the specimens underwent, but with all the safeties off and the process running at full capacity. As Kevin walked out of the test chamber, he knew he had become as perfect as any human could hope to be.
When humans started murdering his "children", he knew that it was time to take the fight to them. Armies fell before him, none seemed to be able to kill him, or even harm him. He would continue his work alone, and create and protect more of his specimens until the day someone could finally work out how to kill him.
This leaves us with the Patriach, a bad motherhumper with a Rocket Launcher, a Chaingun, cloaking devices, mutated close combat weapons, and the ability to call some of his 'children' into the fight to distract survivors until he can heal. Final boss material here, folks.
Personal winner: THE PATRIACH. While the finales, at times, can be atmospheric and awesome, they just can't stand up to the sheer 'you gon git fuk'd' mentality of a Patriach encounter. That and the Patriach has some pretty awesome lines.
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