Years ago, I bought Code Veronica second-hand in GAME, the man at the cash register said “There’s no manual with it, but it’s Resident Evil, played one you play them all.”, and it’s true, multiple RE games used the control engine of forward, backwards, and rotate. Good games, but the engine and concept eventually gets stale after a good few years.
The producer Masachika Kawata has said however if the series didn’t branch out from the survival horror roots, people would be really sick of the series. In an interview with Gamasutra, Kawata said “At the core, basically, we want to make the best use of our brand, Resident Evil is an IP, and a franchise, that people have loved for a long time. It’s still very, very popular and we’re very, very happy about that, and we want to basically answer all the requests that we get about the series. People want to see a lot of different experiences within the Resident Evil universe, and so we’ve been fortunate enough to be able to answer those requests with a lot of different experiences, in different forms, in games.”
Though always a survival horror, the games have departed from the ammo-conserving nature of the original games to being a cooperative online game such as in Outbreak where normal people are caught up in the zombie attack, and Resident Evil 4 provided a completely different engine altogether and a completely different set of enemies and ideas, focusing on a viral parasite rather than the T-virus. You cannot deny that Resident Evil is an excellent series, but running around finding puzzle solutions that make no reasonable sense
He also said “In my mind, we’ve got this online shooter game, we’ve got other things like Mercenaries that are even more action-focused, and some other games. And by going in a lot of different directions, I’m pretty confident that people are going to still be enjoying Resident Evil for a long time”