I picked up the GOTY version of this game a few weeks ago and am enjoying it immensely. As noted in posts above, the story isn't terribly original, but early on in my second playthrough I'm already hearing different reactions from NPCs based on the different choices I'm making in this run.
I'm also still discovering new areas I wasn't aware of in my first run. Like Deus Ex, there are numerous paths to each mission target, and like Hitman Absolution, a lot of different ways to "eliminate" him or her. I'm also seeing a lot of elements similar to Bioshock and Assassin's Creed games, without it seeming derivative of any of them. It's a unique, fully fleshed out world if you take the time to talk to everyone and read the various letters, book pages, and other documents lying about. Whereas only Bioshock's ending changed depending on certain choices made in the game, Dishonored's environment subtly and gradually changes, along with NPCs' reactions and behaviors, so each playthrough is not an entirely linear experience.
I know a lot of people around here are looking for ways to trim their backlog at this point rather than add to it, but I highly recommend this GOTY package that includes all the playable DLC along with the various pre-order bonus upgrades ("bone charm" ability enhancements that aren't available in the vanilla version). I know it's listed in the Gamestop BF ad for $25.
You might be surprised to see how many awards
this game won.