TL;DR
I used to love the game as a child, but I've clearly forgotten how masochistic you have to be to enjoy the infuriatingly slow and wonky animations and zergling swarms of aimbot enemies. Can't really recommend the game even to those whole liked the first game, and certainly not to people who started with the latest third game that has far more polished gameplay.
Story
The brother of the main character from the first game gets murdered, so the main character sets out on a quest to stop a railroad company from killing random civilians with fake Native American attacks on the trail for some reason. Where does the revenge play in? Oh, the guy killing people also killed the MC's brother, of course! If that sounds confusing, it's because the game doesn't really elaborate the position you find yourself in half the time, and the brother's death gets mostly forgotten by the plot.
Gameplay
Desperados II is an isometric real-time tactical game with an added third-person view option, allow you to control characters directly. You control a team of six characters, each with unique abilities or gear, in addition to their ranged weapon of choice. The game tries to blend shootout action segments with stealth-focused segments, but leaves a lot to be desired in both departments.
On the action front, the game changed how aiming and weapon ammos works. Instead of guns being infinitely reloadable but overheating with use, you instead have to pick up ammo from dead enemies... which is only relevant at the very beginning of each level when your ammo supplies are reset, but becomes utterly meaningless after a few kills (excluding Hawkeye, since he can't get more arrows from enemies). Enemy AI seems to only have two modes: braindead zombies that literally limp around the map and run straight into your shotgun, or aim bots that one-shot you through walls and obstacles from a longer distance than you can even attempt to shoot them at. Also, characters can't take out their weapons and move at the same time in tactical mode and tend to get themselves killed before they finally comply with your command to stow away their weapons to beat a retreat. And don't get me started on the aiming and reload system... you need to focus your cursor steadily onto an enemy to shoot them (the farther away they are, the more time you need to focus before shooting), but the characters will randomly start reloading and throw off your aim at the worst timing imaginable. Other times, you'll be firing blanks, because the characters can't get it through their thick skulls to reload already. In short, be prepared for a lot of game reloading.
On the stealth front... it sucks. Since practically none of the characters have any decent lures or distractions, it just boils down to using Kate's seduction to lure people out of sight to knock them down. Technically, some characters have other ways to distract/lure people, but they're very cumbersome, and the knockdown animation is so slow (and characters need to get into a standing position before they carry out ANY action) that you have to mad-dash at a seduced enemy to have any chance of K.O.ing them before they shoot you. And there are a WHOLE lot of enemies on the map, so the stealth approach will get VERY tedious. Especially on the FOUR no-kill-no-alarm levels.
While each character has four different actions available, you'll soon realise that most of them don't have any practical use. Either because you need to get too close to an enemy - that can do 180 turns instantaneously - to use them, or because they're too cumbersome to use without decent lures and it's much easier to just take out your gun and be done with it. There's too many enemies around to use your gear anyway.
Level Design
There are 6 missions in the game, each divided into 2-4 sub-missions, usually reusing the same map (or part of it) as the previous one. Excluding the recycled locations, there are 7 unique maps in the game. In the early game, the recycling of the maps doesn't feel TOO obnoxious, since you're either using different parts of the map, or have story reasons to replay the same area, but in the later part of the game, it turns into horribly blatant padding. Instead of going from point your starting point A to your end goal B, you go from point A to get reinforcements at point C, then the enemies respawn and the reinforcements decide to wait behind as you go all the way back down from point C, but now stop by point D, after which enemies will respawn again, and only now can you go to point B. What's the point of reinforcements if I have to kill off the entire map twice, only for them to die off easily in the end anyway?
Overview
The Good
+Quick Action feature lets you chain multiple actions, instead of just one like in the other Desperados games
+Map rotation
+Third person mode lets you get around some bugs or poor visibility
+The game tried to innovate
+More shooting than in the other Desperados games
+Sam is no longer the only character who can tie up people
+Game shows the effect range for some actions
The Bad
-Lacklustre story
-Recycled levels
-Slow animations, wonky and unresponsive gameplay
-Lack of decent distractions/lures
-A lot of character skills are useless or inefficient
-Enemies are either braindead zombies, or aimbots one-shotting you through walls
-Stealth is handled terribly
-Multiple forced stealth+no-kill levels
-Resolution issues
-Horrible aiming and reload system
-Poorly balanced levels
-LQ voice acting