Can't think of anything on top of my head, so instead I'll ask: What makes you say that Resident Evil 4 is a "masterpiece"? For me it completely ruined the series. It went from survival horror to action shooter when RE4 was released, and every game since has been an iteration of that.

To me that's not Resident Evil. The fun of these games comes from the horror of not knowing what's lurking behind the next corner, and the fact that even one zombie can ruin your night. RE4 removed all of that by placing the camera behind the player, and then turning zombies into cannon fodder that swarm you by the masses. That's not Resident Evil for me, and for that reason I consider RE:0 to be the last good game in the series. (Not including the remakes of course; I'm only counting new entries.)

The thing is, your opinion is the majority. I'm the odd one out here, and I can't for the life of me figure out why. One theory I've been told is that for a lot of people, RE4 was their first Resident Evil game, in which case I can understand liking it if you never knew how good the old games were. I also understand that the tank controls can be off-putting, but that can be bypassed by mapping forward to a button other than up, that way you can move and turn at the same time (also the remakes give you an option to turn off the tank controls). So I really can't think of any other reasons why one might prefer RE4 to past titles.