I agree with Bishop76 that RE5 isn't a bad game, it just isn't a very good game either.
It wasn't just the forced co-op aspect. The whole gameplay mechanics, which were fresh when RE4 came out, felt dated and a bit stagnant, especially when compared to the utterly brilliant Dead Space, which came out a year earlier and reset the bar for third-person survival horror games.
I mean, why the hell can't you move and shoot at the same time? Chris is supposed to be a highly trained BSAA operative, yet he has to stand still every time he wants to shoot something. It seemed like a really contrived way of trying to ramp up the tension during action sequences. Dead Space proved you can create great atmosphere and tension without having to nerf the main character in stupid ways.
Honestly, while I'll be picking up these HD remasters when I can, and I'm interested in the Operation: Racoon City spin-off, the next main RE title is going to have to do something very different in order for me to pick it up. And if there's forced co-op again, I won't be bothering at all.