I've hardly played any RE games, but I'll put a few notes about those that I have.
Also because I have very strong feelings about RER2 haha.
RE5: I played through this one quite a few years ago. What I did like about it is that it wasn't too scary... I am an absolute wimp when it comes to scary stuff, so I didn't mind this so much haha. I don't remember being particularly impressed by it... except for the Mercenaries mode. That was absolutely my favorite part; I would have rather just bought that as a standalone than bother with the main game. It had a nice risk-reward balance with the time markers (though as I recall you couldn't earn time indefinitely, which I think should have been implemented), and the pacing was good. Plus costumes are fun. I really don't know why they changed this mode so much in later releases, as I thought it was pretty great! Despite all this, I will forever hold a grudge against Game Informer and anyone else who gave this a 9/10. I'm not saying it was a terrible, trashy game... but in no universe would I give this a 9. As was mentioned, the forced coop shouldn't have been there, probably. It's certainly apparent by now that working with an AI in games is a design that is just asking for trouble (though, as I understand, it worked well enough in 4 when it was there? If that's the case, I don't know what went wrong.... too much AI, maybe).
Raccoon City: Here's the simple summary... it had good bones in terms of what was there, but they failed to flesh it out, which is part of what made it so terrible. Also, waaaaaaaaaaaaaaaaaaaaaaay too short of a campaign; I think I beat it in like 5 or 6 hours. RC could have been a good game if it were further developed, refined, and tweaked; what we got felt more like a beta, and may God have mercy on those who pre-ordered it for a full $60. For more, you can check out my review I wrote many many years ago:
http://thetabletopcommander.tumblr.com/post/86913047142/review-resident-evil-operation-raccoon-cityRevelations 2: I know people have mentioned loving this game before, but much like 5, I will fight you on it haha.
I bought this for basically full retail price while overseas, and that was a huge mistake. I don't think I got through the first three chapters, because I found the game to be so boring and tedious. I just couldn't invest myself very much in the story (though to be fair, I haven't played any of the other games really, so it'd be hard to get invested). I tried playing with a friend, with no improvements. I couldn't imagine having bought these episodes separately for the price they wanted originally. Kind of like Racoon City, I felt like there was potential, but the game was just poorly designed and executed. When a game that is basically made for couch play doesn't improve when played on the couch with a friend, there's issues.
I could, however, overlook all of this if the Mercs mode was good (since that was basically the reason I bought it)... buuuut it's not that great. It's not terrible, but it needs improvement; it doesn't feel very compelling to play. More random enemy generation would be nice, and again, I'd really like to see the time trial stages return. I just don't get why that was eliminated. Also, if you play with two people, you have to be incredibly careful about ammo consumption.
Also, better costumes.
I'm skeptical about the new one, but we'll see.