I wondered how silly I would look if after all my defending of the demo I didn't end up liking the game... But I do indeed like it. I don't think I like it more than Binary Domain right now, but I like it. Especially the Chris/Piers campaign (@ Chapter 4's start atm. Chapter 3 Jake, Chapter 2 Leon.)
What I don't see this game getting enough credit for is how it crosses campaigns. Putting aside how difficult it might be to find other pairs in the future, the design around it is smart and the concept is very novel. Probably the funniest experience I had playing this game was someone with a mic losing his shit over this. "This game got four man co-op? OMG!!"
This is on top of how good co-op is designed (in Chris's campaign, anyway). I get a lot of satisfaction sniping as Piers, covering some dude I picked up online. I always felt RE5 was above the caliber of typical co-op, and they took it to another level with this one. As far as I am concerned there should be no nagging on the fact these games have co-op. It is not shoehorned and this is an advancement on the idea.
One of my biggest gripes with the game is how confusing I find joining a game late. I rely on this mainly because no one ever joins me in my lobby and rarely do they join me in the middle of a game (and I'm not playing this co-op offline yet because I don't want to wait on someone).
So the main problem is... I've never gotten credit for clearing a chapter unless I was there from the beginning (which means taking part in the chapter before). What am I missing? That would be quite a poor design choice to punish joiners like that, especially since you can't filter it by lobby. Not understanding this (and experimenting with it) has lead me to replay missions. I ended up doing Chris Chapter 2 like four times lol... I've killed a lot of Ogromen, or w/e.
Also you seem start with very little ammo after wiping your progress (in other words: switch characters/campaign). This comes up a lot if you are playing the game by the order listed in the OP (for the storyline or w/e). I really noticed this in Chris campaign where the game is clearly designed around Piers using his sniper rifle to get rid of turrets, snipers, and RPGs (among other scenarios). Dropping yourself right into a game in progress (though the beginning of Chapter 2 counts too) with zero sniper ammo sort of breaks the design I'd say. So with that in mind I can't recommend playing this way. One of the ways I have adapted to this is equip the drop increase skill.
One unimportant thought I'll just squeeze in... if Capcom was really smart they would have ended the prologue with both characters being brutally (gore-y) killed, giving the player the idea that he was leading his characters into a hopeless situation.
EDIT: If you are playing this on Normal, then you made a poor choice I'd say. Just by judging the main game vs the demo, you really see why this game is meant to be played on Professional, if not at least Veteran.