First off, PC or Console version? If console, no don't bother.
If PC, read on:
1. An honest to god interactive story. Remember all those blurbs you read on the backs of other RPGs that claimed to have interactive stories and were bullshit? Yeah, AP don't play dat' shit. Your actions have consequences, change the story and the outcomes. This is super-duper true for the ending sequence. I won't spoil it though! Plus the game will tell you at the end of missions what your decisions were, and what effects might be. This makes it a bit easier in subsequent playthroughs to do things completely different.
2. The skill system is a bit wonky. You MUST specialize in some sort of gun, and at least 2 points into the tech tree (for added times on the minigames), otherwise there are points in the game that you will be F'd in the A.
3. Building off that, Stealth is broken. In the beginning it kinda sucks, near the end you are a nigh-unstoppable killing and stealth machine, except bosses, who dont care if you can stealth. Up to you whether this is good or bad.
4. The gameplay is like an odd cross between Splinter Cell, Mass Effect and an evolution of Deus Ex. Its primarily sneak oriented (though you can run and gun if you please), but you have activated abilities with cooldowns that allow you to do extra stuff either with your weapons or with special items like flashbangs or what have you.
PERSONALLY, I find it to be an excellent game and I've had a lot of fun with it (I've beaten it 3 times now), so if this sounds cool to you, I say pick it up.
If you have any questions, feel free to ask.
edit: Oops! Forgot to add, on the technical issues-
The reason why I ask console or PC in the beginning is because from everything I've read the console versions were marred by a lot of bugs and glitches, and Sega said no to Obsidian doing any patch support for them, so its probably still broken.
For PC, I played it on release day, and I only hit one bug, which is where if you wear certain kinds of hats with crazy hair, if you then take the hat off it will default you to the buzz cut hair, and you have to switch it back.
Only bug I hit in the whole damn thing, with 3 playthroughs.
So, keep that in mind.