Replayability should be a key factor in a game like this. The game (speaking of what I've seen, I've not played it yet) kind of reminds me of the VR missions of the MGS series, because of its "challenge" structure. I'd like to see more of this action-puzzle games (I see the Hitman series as one of this new type of games too, as each mission requires more thinking and planning than shooting to resolve it).
"Acquired" the game a bit ago, and played through Episode 2. Once again I'm amazed, intrigued, and impressed. I really like the atmosphere of the game/soviet bloc-type architecture. The story is also some of the best writing/storytelling I've ever seen. Getting out of the car and walking around the White Forest Inn... you can almost feel there, the atmosphere and environment are so real. The graphics are just icing on the cake, I think the design lends a lot to it. I will definitely be buying the retail game for the rest of the games.