Note: I won't put plot spoilers in here, even enemies will be left out because some will bring a heart felt smile back to your face :D
The experience was very enjoyable, specially after the half-way point where it kicks into being just an absolute blast to play, incredibly awesome singleplayer/co-op experience!
I would say compared to most resident evil games that the story in this one isn't the best but its surely not the worst either. You'll be left with a feeling of wanting more as some things are left very under developed, if you can consider resident evil 5 anything its that its the end of a story arc in the series and when capcom says that the next game in the long running series will be a new chapter in the universe they pretty much aren't kidding because they will have the freedom to work from the ground up on gameplay and story with resident evil 6.
I can say without a doubt sheva is a stupid character in the gameplay and plot department, don't bother giving her anything but pistols, sub-machine guns or the bowgun, this is one trigger happy biatch!
So during the game I avoided giving her...
Magums, Rifles, Assaults Rifles, Shotguns, Explosives, Etc
As a gamer you don't want to give her anything that you find highly useful and has very limited ammo supplies because she chews through anything you give her without concern for supply or situation, use her effectively as a pack-maul and a backup shooter, never rely on her as your useful tool because she will get you killed more then times then anything else, yes when she dies, you die!
When it comes to co-op with a friend make sure to play on each others strengths, don't worry about your weakness just abuse each of your strengths to death, if someone is better with range give them it, if they are better with handguns let them have the majority of the ammo, if you can throw explosives better then hog them.
Never be friendly online unless you know the person because they aren't going to give two-ticks about your own situation, they'll try an act like rockstars, sadly if they die your up the creek because they'll constantly keep getting you killed, these newer players online are terrible, little winny children that just think about me, myself and I, play with people you know because it makes the experience much better, I didn't have the luxury because of circumstances.
I got lucky in that I managed to play one whole co-op game with a reviewer who will only be known as "the g-man", he was awesome fun to play with and surprisingly enough was british, so me playing chris and him playing sheva was pretty funny, specially the conversations.
Do know I've played this four times already (so I've unlocked everything already), yes I've had it far longer then all those other randoms that picked it up in the last day or so, I got it about a week and an a half-ago as a "special care package" (Its not a retail disk, but none the less the full game).
Back to the Game...
People that complain about the controls, if you find the start of this game hard then your going to scream bloody murder later in the game when you really need faster reflexes then the game can give you, this is probably on purpose knowing capcom because if we had perfect controls that were made for these situations then we would chew through these guys like nothing, at least some of them (some of them can take a beating know only to most mini-bosses and some of these are considered regular enemies later).
Merc's is back but your only going to get the main characters to play and when I mean main characters its only four of them, although you will get to play them in different outfits and those are very limited as well :( Compared to resident evil 4 though its bucket loads harder with the new enemy combinations and enemies themselves. So limited in one respect but it still retains that very element that made it great and improved it with gameplay.
Speaking on unlockables they themselves are limited, after you beat the game you don't get much outsides merc's, outfits and some new weapons. Theres no side missions or the like in comparison to the last game, they've skipped out on many of those things which I would say will come with the dlc and I'm fully expecting lots of dlc for this game.
Its really hard to say anything more outside this dribble because you basically have to go into the plot from here which leads me down a path I commonly try to avoid when writing these things, I will say this though that its going to be very interesting how they proceed forward from this game to the next because it could either spell total renewal of the series or absolute utter total devastation to it with no way back.