Everyone always regards 4 as an evolution to the genre and revolutionary.

Ironically it mainstreamed a lot of design ideas that people now complain about, like quicktime events and contextual button presses (actually do people still complain about that? I know they used to after quicktime events got shoehorned into everything for like a decade after RE4). Basically everything about its design and controls was practically cutting edge for the time, even if it didn't invent any of it itself. I don't particularly like RE in general, but RE4 was genuinely an important practical example of a bunch of design principles that have since become standard.