Everything everyone says and more!
What Arkham City did for game-play (just a year and a half ago!) this did for story; if you know me, I mean this as the highest praise. Never a second went by when I wasn't wrapping my head around new events and themes. While the graphics are not the most technically proficient I have seen, they are perhaps the most gorgeous I've seen. While FPS gun-play is not my biggest cuppa tea, it is made interesting through diverse and useful powers. A further comparison to Arkham City: Colombia is a real place. While you are playing, you are in a different world, one you might like to visit despite is numerous troubles, simply because it is that real and fantastical. The characters there (note I say "there" not "in the game" since Columbia is real to me) bring the city to life, Elizabeth especially so. Everything she does is so natural it's easy to forget she's a piece of AI.
I'll end my rambling praise and leave you to play it yourselves. It was worth the $60 to me to play the game before someone spoiled it all.