I loved it. I don't care what the critics say. It's not the longest game around (not like Morrowind / Fallout 3 scale), but it's got SO much more replayability.
If you're prepared to do different things, and solve puzzles differently (and unlike other games - you actually CAN solve the puzzles other ways!), it can be a completely different gameplay experience (although the story will remain broadly similar).
Most 'multiple game-style' games tend to be poorly designed. You get WAY more experience hacking your way mindlessly through the various goons than you do if you cleverly stealth past 'em. That's largely solved in AP - I've never felt I'm gimping my character by NOT killing the goons!
Having played most of the Bioware and similar games (ME2, DA:O etc.), this is the only one where I've really experienced replayability! I'm on my 3rd run-through since I bought it (shortly after release, so about a month) - and still enjoying every minute. I particularly enjoy discovering the effects on later missions that my earlier decisions make!
I'll admit it can be a little buggy, and I DETEST the console-based 'save points' system (although I can see why they did that one - to prevent the save-reloaders that are so prevalent in PC games), I'd still totally recommend this game to anyone who's even vaguely interested in it, or wants to try something a little different.
And here's a free tip : Unlike pretty much all RPG-FPS games, ALL the guns are useful (although I'm still experimenting with the SMG's). Even the combat will play differently depending on your weapon of choice!
In this game, there's not much a room full of baddies can do when you pop a flashbang and charge in with a tricked out shotgun! The knockdown feature will keep pretty much all of 'em down. Play with a silenced pistol, and you'll be headshotting / tranq darting your way through the level like a ghost. Grab an assault rifle, put a decent sight on and boost the accuracy, shove sub-sonic rounds in, and you've basically got yourself a suppressed sniper rifle. Use ordinary rounds (and stick a few mines along the corridor) and you can create an absolute killing zone for enemies to attack you from!