I preordered the 4 pack close to 2 weeks ago and i've been playing it ever since day 1 and i can safely say, i'm nowhere near stopping. There's so much to do, and so many weapons to find and so many skills to obtain. And each of the 4 different characters gives you a different tactical approach.
About the gameplay, its pretty much similar to the console versions, nothing fancy there, except the fact that the dev have hinted at mod support (look at my sig

) and it looks oh-so-awesome with all details turned up.