you SHOULD have played this allready.
It does everything correctly and everything it does is awesome. That is the short version.
The longer version:
JC Denton is the main character and who you play, he is an augmented new generation of Nano-tech soldier whose training and augmentations allow him to jump higher, run faster, hit harder than a regular person and a 2nd generation augmentation soldier/agent. Basically you are a superman that can control how you play, take out objectives. I shall talk about that first.
The nano-tech is one aspect of the game that gives it high replay value if nothing else in the game takes you (which i would find hard to beleive). As the game progress's you find canisters that allow you to upgrade parts of your body such as legs, arms, heart, lungs, head, eyes, feet, hands, chest...i think thats the lot. And each upgrade gives you 2 options such as the Lungs allows you to pick EITHER aqua lung that gives you a longer ability to breathe underwater for longer OR an ability to breathe in hazardous chemicals.
Each upgrade has 4 levels so the more you upgrade them, the better they work and give more options. Such as your eyes could allow you night-vision, then upgraded to nightvision+infrared, then NV+IF+sonar (see through walls) THEN NV+IF+Sonar+stronger Sonar.
Along with the Augmentations, you gain skill points for completing objectives. These skill points can be spent on skills to increase your general abilities so that they unlock other abilities once upgraded by spending more points into it. So a skill starts on untrained with basic ability at performing tasks, if you upgraded it becomes Trained, then Advanced then Master.
An example would be computer skills where at first you can hack into a computer system, if you upgrade its a more secure hack, upgraded again you can hack+control security to an extent, upgraded to hack+security+turrets and bots!
Computers and electronics and lockpicking and demolitions all mix it up with your choice of weapon skills. Heavy, Rifles, Pistols, Demolition are all fine but the most fun being Low-Tech which is fire extinguishers, throwing knives, pepper spray, tasers...it goes on and on and coming up with ways to neutralize your oponents, giving you that reload factor as it goes wrong or wonderfully right so you want to do it again. Oh i will say this, it is possible to go through the entire game without killing (nearly all of) your enemies.
So yea, there are many many many options to play JC Denton but the real reason to play is the story. It truly is amazing and in-depth. Seriously multi-layered with hundreds of additional text to read if you feel like it. There is actually a fictional book in the game that if you find all of the chapters you end up reading a full sized book that i guess, inspired some of the story telling within the game.
As an agent of UNATCO you find yourself fighting terrorists and working for the goverment on various tasks. This quickly slips into a strong mix of conspiracy and hypocrisy mixed with a dash enviromental issues and a pinch of working Vs upper class. There are so many references to history that you are actually learning about American history and French history as you play. To make this game even more awesome, the voice acting is seriously great. It does not ever seem camp or lame or weak, its full of expression and cool and just done perfectly. I can still hear JCs voice whenever i want to and his voice is just one of many many great actors in this game.
I will not and refuse to talk about the plot any further because i believe it deserves your full attention and i will not ruin it for you.
Along with the endless combinations of customisation and the great dialogue and masterfull prose, you play and fight around the most amazing locations. From the ruined statue of Liberty, to the streets of Hells Kitchen in NY, to the back streets of Hong Kong, to the corporate towers, to various military bases you are never left feeling you have ever been in these places before. Finding the most sneaky ways into these locations and around these locations becomes an art. The most obvious way is not always the best and there is always at least 1 other if not 2-4 ways into and around these locations giving you again, more and more options.
I truly love this game, its far too big to include everything i want to say and i feel i have gone on a little too much so i will leave it and make your soul decide if it wants enriched. Get this game to save your gaming spirit, get it to increase its strength and get it so you can include yourself in an fraternity of players who have played it before you. Buy it and play it right now. Please.