Short and glitchy, but nonetheless fun to play with a friend.
As an example, there is one particular section in which the main characters are split up, one of them doing the front-line fighting while the other snipes. The fighter will come across a turret that is hidden from the sniper by a thin wall. The fighter then has the option to "tag" the turret operator, making him show up on the sniper's HUD, allowing the sniper to pick the operator off through the wall. The players are not explicitly told to do this, however, making the collaboration all the more satisfying when it pays off.
Moments like this are far too rare, though. For the most part, you will just be running and gunning through areas littered with convenient cover, employing flanking tactics only when a heavily-armoured enemy shows up.
The heavily-armoured enemies were another problem of the first game. Having no armour on their backs was just such an arbitrary weakness. In The Fortieth Day, this problem has been rectified. Heavy enemies carry big weapons that require a lot of ammunition, and carrying so much ammunition requires that they have a pack, or satchels of some sort. It is these packs that you are required to shoot repeatedly, causing them to explode. This system is far more believable, and satisfying when you see the gatling gun-weilding psycho explode.
The story is haphazard and entirely forgettable (not unlike the first game). Tyson Rios and Elliot Salem have started their own PMC, Trans World Operations (TWO), and for no clear reason they decide that the best place to set up shop is in Shanghai (leaving aside the fact that the Chinese government would never allow an armed American organization within their borders in real life). Sh*t hits the fan when a hitherto unknown army composed of soldiers from various ethnicities (so as to be politically correct) attacks the city, blasting it to pieces under the command of some American (again, for political correctness) nut-job who spends the entire ending pontificating half-baked platitudes of human nature and nobility. There are so many plot-holes, I don't even know where to begin.
Given that this formerly civilian area has become a war zone, Rios and Salem have many opportunities to save hostages from the attacking forces, which plays out the same way almost every time: One player sneaks up behind the commanding officer and grabs him, forcing his subordinates to surrender, allowing the other player to tie them down. It gets old, fast. Slight variations occur in which you have to silently take down a soldier who is between you and the commanding officer. Sometimes if the hostages and captors are too far away, you don't even bother with any of that and just snipe all of the enemies. These occurrences are a nice change of pace.
A new addition to the game is a morality system. Rescuing hostages adds to your morality points while letting them die detracts. But the core of the system revolves around rare events in which the players are presented a 'co-op morality choice' that will offer certain rewards and trade-offs. You don't actually get to role-play, though. When you let a child die in order to acquire a new gun, the characters don't behave as though they did it deliberately because they're selfish pricks; they just chalk it up to an error in judgement and move on without any changes to their personalities or the story.
The gun customization system is insanely deep. You no longer have to buy the cheap suppressor before you can get the good suppressor. In fact, you may forego a suppressor entirely in favour of a bayonet. The most expensive parts are no longer de facto the best ones as every part has certain advantages and drawbacks, and you will be messing around with different configurations for your favourite gun even on your fifth playthrough.
The fact that no element is overdone means that The Fortieth Day has a lot of replayability. Finding all of the hidden weapon parts will keep you coming back (there are also radios and porcelain cats to collect, but they're much easier to find). And getting the 'The Beast' Achievement will require approximately ten playthroughs.
The biggest glitch I encountered was with the AS-KRI, the best assault rifle in the game. Buying it costs $300,000 (not a small price tag). Once I'd bought it, I tried it out for a while, and then I went back to my preferred firearm. The next time I checked, I had to buy the AS-KRI again. I did so, used it, unequipped it, and then I was asked to pay for it a third time. If you unequip the AS-KRI, you lose it. I am hoping that this gets patched.
The campaign is way too short, but considering the amount of replay value, this is not a huge concern. The AI partner is decent, and the commands you can issue to him work pretty well, but he will occasionally do something entirely different from what you want him to do, and there is nothing that you can do about it. This game is definitely better played with a friend, and played repeatedly. It's not perfect, but it's fun, and what more could you want?