I just finished the game, it took me about 20 hours without much rushing (read every mail I got, read the mission debriefings, listened to most of the news). The game certainly isn't the longest RPG out there, but it's not terribly short (for comparison: ME2 took me 25 hours, Dragon Age 55 hours).
AP certainly has it's weak points, the enemy-AI varies between fine and laughable, the hacking minigame is atrocious while the other two minigames are ridiculously easy and I'm not a big fan of the interaction point stuff instead of giving the player free roam of the levels.
But AP succeeds in telling an interesting story filled with interesting characters (most of which you can kill, yay ) and offering the player a lot of choice. Both regarding his playstyle and regarding the route the story takes. I certainly will play the game at least once more to try some other choices along the way.
The shooting gameplay isn't the most polished I've seen, but it works decent enough while sneaking is a bit more erratic (although I have to admit, that I didn't put many points in sneaking, will do that next time). On the other hand updating your various weapons and gear is a lot of fun.
To compare the game to it's nearest rival: For me AP is the better game than Mass Effect 2. While ME2 has a lot more polish and the shooting gameplay works better Bioware threw out most of the RPG-elements which made ME1 fun and the main storyline of ME2 is laughingly bad.