RE5 has superior replay value, more collectibles and unlockables, better Mercs mode (being online), and more tight controls. However, it isn't as well designed as RE4, lacks its hilarity and AAA script, difficulty, and sense of isolation. RE4 is best game all time material. RE5 was just goty status. That doesn't make it bad though. No game I replay 5-6 times with a clock of 50 hours can be bad.
I can understand not liking RE5 as much as 4. I don't either. But the endless hyperbole surrounding 5 is annoying. Speaking as someone who 100%d the game without touching co op once I think a lot of people discredit the game without any merit.