Army of Two was a title designed from the ground up for Co-Op Play.
I really think that perhaps, this intermediary step between that is part of the problem. Most people have a problem playing single player in co-op games when their AI partner is dumber than a fish on a wall. The AI simply doesn't behave like a human would, they don't do their job, and for the most part, players need to compensate. It makes their experience that much more difficult because they are "babysitting." But if you realistically think about it, thinking back to a game like Modern Warfare 2, are there not AI guys with you at all times? So how is that any different?
Games like MW2 do a good job of hiding what the AI is actually doing behind scripted events. While it may seem like your squad mates are doing a good job covering you, those guys they just "shot" - they were going to die regardless. They didn't cover you at all, and the next time you replay that section, it'll happen the exact same way. Perhaps this is why a series like Halo has always done so well in co-op AND single player, because it mixes and matches these two styles of play together.
In Halo 3 you can play the entire game by yourself, at times being joined by AI guys who do behave realistically in terms of their actions with the game world. They also make mistakes, and these mistakes give them a human like trait that is intangible. But Halo 3 also allows you bring in other players to help you - and sure - it doesn't make sense in terms of the story. But it's still an epic experience, and each person is on their respective couch enjoying it equally. They get the same cinematic presentation, they get the same sense of satisfaction, and they get to enjoy that with a friend.
So was Capcom wrong in their design decision for Lost Planet 2 and Resident Evil 5? Probably not. They took the risk of listening to feedback and now they'll see if the reward pays off. Of course you're going to piss off people like Patrick Klepeck of G4TV along the way - it happens. But any revolution is going to be difficult at first, and perhaps the Co-Op Revolution that we're seeing now is best described by Penny-Arcade's recent news post about Lost Planet 2.
This is a game that needs to be batted back up into the air, reintroduced to the discussion. I've had experiences in Lost Planet 2 that put it very near the top of this year's releases...
...and hearing that a co-op game is best played in co-op ain't exactly front page material. "We" have "said" for years that we want meaningful co-op experiences, but when they're delivered to us, they must give an impeccable single-player performance as well?
It has grand ideas, and longs to show you them. No, it's not perfect. How could it be? This is how the future happens, sometimes; it comes in fits and starts.