Invisible War is the sequel to Deus Ex, one of the most lauded PC games of all time. As such, it was burdened with almost impossible expectations even before announcement. And it has since been largely disowned by the fanbase for not living up to the precedents that the first game set in terms of a dynamic world that responds to player action and choices, for taking a more Halo-esque "shoot first" approach to the level design, and for just kind of generally derailing the story.

And it deserves criticism on all those points. However, it's actually a well-better-than-average FPS on the whole. Had it been released as a separate game with all the Deus Ex references scrubbed out and some new name, it wouldn't be on anyone's Top 100 lists, but I think it would certainly be generally well regarded by those who had played it. It's a "glass half full or empty" thing, really. As the sequel to Deus Ex, it's disappointing. Taken with the expectations of the standard FPS, however, it actually does quite a bit that your Halos and such don't even aspire to, and is largely pretty fun to play through.
 The game takes places 20 years after the first in which all three of Deus Ex's possible endings have basically been smushed together so that technically they all happened. JC Denton merged with Helios in an attempt to create the perfect automated democratic system, but in the process also destroyed Area 51 causing a Dark Age in which all global communication was taken out. High-tech made a pretty fast and impressive rebound though, as now most of the developed world is under control of the WTO, who enforce a hyper-capitalist system with their massive private army. You play as Alex D, in either male or female form as you prefer, a nano-modded student at a WTO special forces academy who gets caught up in a terrorist attack which in turns leads to all sorts of further twists and shenanigans. I picked the female version simply in protest of the douchey cover art, but apparently the guy's voice acting is way worse as well.

 The initial confrontation is between The Order, a "unitarian" religious cult using terrorist tactics, and the WTO. For the first half of the game or so, you're basically choosing to help one side or the other. Later on other factions are introduced however, such as the Templars, a populist movement that wants to scrub the world of all augmentation, and ApostleCorp, a shadowy research company.

One of the game's selling points is that you're largely free to choose your own allegiances as you play through, and can switch as you go, gaining differing mission objectives. However, this is a lot more linear than it sounds on paper. Each level and area generally has the same objectives regardless of who you are working for, there's just a binary goal - for example, one group wants you to find a scientist and question them, the other wants you to find the scientist and kill them. The game also leaves allegiances open by having the factions basically forgive you for anything you've ever done for them in the past as soon as you agree to take on a current mission for them. And regardless of how many times you betray their trust, up to the end you can still keep working for them.
 The other thing about the game's allegiance/morality system is that all of the sides involved are pretty scummy in their own way, and your choices nearly always devolve to a greater or lesser form of thuggery. I didn't want to work for either the WTO or the Order, but to progress in the game you have to do things that either one or the other will automatically claim for themselves. I was choosing mission approaches based on my own moral compass rather than allegiance to one group or the other, which sent me illogically pinballing back and forth between them for the first half of the game. And all the side quests are just blatant random thuggery and casual murder for extra money and weapons - murder a lawyer in his house, get in the good graces of a club owner then narc on him, burn a coffee company's bean supply for their rival, etc.

Really the first half of the game or so is Deus Ex: Hired Goon more than anything. Eventually the story gets on a more even keel when you discover the true natures of the WTO, the Order and ApostleCorp, and then it starts to feel both like the game has a meaningful overall narrative and that your choices actually mean something rather than just holding your nose and picking the least repellent path to progress the game.

 To describe the gameplay, basically the RPG elements have been greatly downplayed and the FPS element has been amped up in its place. The experience and level-up system of skills is completely removed. Nanoaugmentation abilities are still present, but you get nearly all of them from the start of the game, and they are upgraded to max in short order as you're practically tripping over upgrade canisters every five minutes.

There's no more location-based damage, with the exception of an instant kill on non-armored characters for a sniper rifle headshot while using the scope. You have perfect aim from the beginning, and while stealth gameplay isn't totally eliminated, it's greatly reduced in effectiveness and necessity. The stun prod seems to have been thrown in just for continuity, in this game it just kinda tickles the enemy for two seconds and does nothing else. The baton, crowbar and electric sword cannot be used for instant takedowns from behind any longer, as each takes about 80 whacks to bring anyone down even if you ambush them. And there's a form of the crossbow called the "Boltcaster", but it's next to useless as it takes multiple shots and a solid 30 seconds of waiting to tranq anyone to unconsciousness.

The FPS element is much smoother due to the accurate aim from the beginning and better interface, but there's little in the way of different "builds" of characters like there was in the first game, and the way the later levels are designed you're essentially forced to Rambo John J. everyone anyway.
 So a lot of that was pretty negative. So what does work? Well, a few little hinks aside, the game's engine and interface are pretty well done. While the tone doesn't stay consistent with the prequel, the game world is nevertheless a fairly interesting cyberpunk dystopia to explore. It has some great characters, and while the ongoing story is disappointing as a continuation of Deus Ex, on its own merits it's pretty decent. And though the levels aren't as well thought out as those of the first game, they're still pretty well designed with multiple approaches to most problems, and multiple possible responses from different characters depending on your actions. And generally the gunplay is pretty satisfying, which is good as there's a lot more of it mandatory in this one.

The major issue with it is just that it's so dated in style, I'm not sure how much appeal it would have to someone coming back to it now, and the established Deus Ex fanbase likely already hates it beyond the point of tolerance.

 Links : 
 * Planet Deus Ex 
 Videos : 
 * Gameplay Video