The downfall for what you thought RE should be maybe. But critically, and sales wise no.
RE5 is a very good game, that sold well and was critically acclaimed. it's just not scary. It's a more actiony version of 4 with better action. But worse atmosphere.
It's definitely a co-op game with Sheva's terrible AI. So if you don't like co-op the game isn't near as good.
One game that has issues (RE6) does not a downfall make.