Not that bad, actually.
I played it on the 360, and I think it's a great 3 day rental (or 2 rentals if you're busy).
Pros:
1.Truly open ended story, dialogs and courses of actions. Pretty much everyone and every organisation in the game can be with you or against you, depending on your actions, and if they are backstabbing bastards (and since it's an espionage story, everyone is a backstabbing bastard to a certain degree). You have 5 main "location chapters" (kinda like KOTOR) with the middle 3 that can be done in any order. But with the difference that you will meet some of the same characters and organisations in more then of them, giving you a truly infinite amount of story possibilities.
2. Backstabbing: Like I said earlier, since it's an espionage game, you can (and will) have to back-stab people to reach your goals and will realize that sometimes some radical terrorists, some rogue psychos and some bloodthirsty mercenaries aren't that bad (depending on the point of view) and that many of the "upstanding", trustworthy and good people leave only death and chaos in their wake. Characters might cross the line between friends and enemies many times.
3. Fun and challenging: The game is full of hilarious jokes (like when you fight a crazy drugged mobster playing 80's rock music) and challenging decisions and situations that'll have you think rather then just move and crush everything in front of you like most modern games.
Cons:
1. CHALLENGING: This game is hard, even has a soldier, you'll face ridiculously tough bosses. Example: You will fight against M. Bison from Street fighter (ok, not exactly, but he looks and fights like him), who can unleash a terrible unblockable 5 punches combos that'll take away most of your health (pretty rough since this is a shooter) while black ops soldiers come from every single direction to kill you. Prepare to die many times. If you want to live, (and have fun) play has a soldier, and specialize in assault rifles.
2. Bad AI: It's not that bad, but expect to fight dumb expendable mooks with little survival instinct and pattern based bosses. It's old school! So dont expect Splinter Cell or Modern warfare AI.
3. No multiplayer, and quite unrealistic RPG aspects: This isn't a fluid shooter like Mass Effect 2 or Gears of War. So if this is a problem, I dont recommend you play it.
In summary, it's like a mix between the first Mass Effect clunky third person shooting and dialog tree, and the Obsidian style great open ended elements and funny dialog. While in a cool Bourne Identity / James Bond spy thriller. It's worth a playtrough.