Resident Evil had a very obvious tone shift in the middle of the series, dropping survival-horror in favor of something a little more action-oriented.
Shinji Mikami, in an interview with IGN, explained that the change was due to the poor reception that the Resident Evil remake had on the GameCube. Apparently, the remake did poorly in sales and Mikami opted for a genre that would be more of a crowd pleaser. "Because of the reaction to the Resident Evil remake," said Mikami, "I decided to work more action into Resident Evil 4. Resident Evil 4 would have been a more scary, horror-focused game if the remake had sold well."
Of course, this experience that Mikami's had with the remake is probably going to carry over to his new IP, The Evil Within, which seems to be a return to the developer's survival horror roots. "I have kind of a lingering trauma there, because the Resident Evil remake didn't sell – much more than people would think," said Mikami.
Thanks, SplatteredHouse and Joystiq