SO I'M GONNA DO IT NOW
To start us off, let's provide some initial info: Resident Evil 4 is an over-the-shoulder third person shooter, ditching the traditionally more reserved approach of old horror games to lean into full-on action. The plot follows the adventure of RE2 protagonist Leon Kennedy, on a journey through rural Spain with the mission of rescuing the US's president's daughter. Classic RE shit. You know the drill by now.

What makes RE4 legendary in gaming history is not only being an incredibly good game (and a deceivingly tense one)
The reason it's so respected is context.
RE4 came after the frankly not that interesting RE3 and Code Veronica with a complete ground up of the series. And, much more importantly, a complete ground up for the industry in general: both on a gameplay level, with its over-the-shoulder TPS formula influencing virtually every single triple-A noscript that came after it
And on a technical level, with graphics well worth calling "Next-gen" (that is, mostly very brown).