I played a good chunk of this today and have enjoyed it. I have played on the default difficulty and have completed 2 of 3 zones I have found. 2 of those were red zones, one was yellow. I'll get to the ways they differ in a bit.
Yes, it is a bit Far Cry, mixed with Dying Light's parkour/world navigation. Yes, it is a bit hard at the start, but I feel a lot of that is due to how people play it. It's more FC2 in that if you run around in the open you will be shot at from all angles and end up dead. You don't get unlimited health, nor regen, which I like. Health is found or bought and rarely found on enemies/allies. You are expected to use hit and run tactics and use your allies. You can recruit 3 of them and have them follow you around. They are not smart but do not randomly engage. Think of them like a squad you set up to cause havoc so you can flank/sneak past. TBH, I feel like there is a certain point when in a zone where the game goes from hard to too easy. Once you have won the hearts and minds, aka, morale, of the zone, and taken a good chunk of the enemy camps, you are basically uncontested and can also expect allies to join in when you get into fights. In the yellow zone, this is even more apparent as rioting breaks out and enemy presence goes to defensive mode.
Your weapons are set up with the main, sidearm and eventually, rocket launcher. As been said, you can adjust your weapons on the fly, although it does take a few seconds and can leave you dead if you pick a bad spot/time to modify the gun. Your modifications are 3 per variant. Battle Rifle/Marksman/Freedom Launcher, Assault/LMG/Limpet mine launcher, Shotgun/Assault shotgun/Inferno gun and Crossbow/Flamethrower/Blunderbuss. You need to go to a weapon's cabinet to change your main, so no swapping shotgun for assault rifle mid battle. Beyond that, you have the attachments to buy, gear for your character, and unlocked equipment/weapons via KPA points (basically awarded for certain outposts) and consumables. You can also upgrade the weapon's handling and reload speeds. In some outposts, you can also take on side missions (basically kill x with y, take pictures of x, find y on the map) which pay out cash and expand the game beyond run and shoot.
Early on, I found it tough going with only the SMG, but once I got the battle rifle, I was able to hold my own and still use it as my main due to it's damage output compared to the AR.
Now, I have found the red zones fun in their own right, but yellow zone is where the game should have begun. Here you have to play it more like a stealth game, especially early on. You can holster your weapon and are encouraged to mingle with civilians and can also hide in some dumpsters and outhouses. Cameras are everywhere and if shot out, result in a patrol to investigate. If spotted, the reinforcements come and you have a limited amount of time to either hide, run or take out any NKA around to reduce the alert. Enemy AI is decent and will generally investigate both vertically and horizontally from your last position, but not so godlike that you taking out a lone sniper brings the whole army down on your head. You also have to raise that morale up, and you have a handful of ways to do so, with x number counting up to a point. Then it lets you trigger a full riot in the zone and the NK goons go on the defensive. The RC bomb is fun here and vital.
As for a review, I am enjoying it as a rough Far Cry like game with decent gunfights and content, but expect to see a lot of bland environments, both in the red and yellow zones. I don't know how much of the game I have finished in 13 hours, but I feel like maybe another zone will be after the one I am in. It's not stand out in any regard but is not broken, at least for the R9 290 setup I have.