As far as ambient/cyberpunk style electronic soundtracks go, Deus Ex Human Revolution is certainly one of the best. I've been a fan of the main theme song "Icarus" since the debut of the amazing cinematic trailer from Square and Eidos from E3 '10, and have been eagerly anticipating the soundtrack. Let me tell you, if you're a fan of this genre of music, as I am - It does not disappoint.
The first track on the album "Icarus-Main Theme" is by far the catchiest tune and the main act of the score. Delivering a religious tone and a moody/futuristic atmosphere--complimented by the synth arpeggios, and eventually percussion's alongside additional instruments and choir to formulate the final result. I think I've played this song for almost everyone I know(yeah, I've been listening to it a lot..), and I always enjoy hearing their reaction. "Wow, this is from a video game?" "It sounds like it's from a movie." A friend of mine actually purchased the game after listening to the soundtrack, interesting how that works.
One thing the score does amazingly well, is help you recall your experience with the game. Whether that be the poverty stricken streets of Detroit, the battle with Namir, or the wealthy neighborhoods of HengSha, China. The first time I heard "The Mole"(Great track btw) I recognized exactly where I've heard it at Sarif's Manufacturing Plant. That shows how well the tracks compliment the environment--which was McCanns intention. He states that he really intended for the music to exists "Inside the game". As opposed to a non-immersive track sitting on top of everything else. Not to mention he wanted the music to be nonjudgmental; what one person sees as good another may see differently, and the melodies shouldn't take sides or imply which decisions one should make. I think he succeeded at that.
The music in each area of Deus Ex:HR is composed of three layers: ambient, tension, and combat. Which are added upon each other depending on how intense the situation advances during the game. McCanns approach wasn't to create catchy melodies or overwhelming scores for every section in the game, but to create smaller cues built around the player and the environment to express the emotions surrounding that specific area. While I can agree that the music is better suited inside the game with the elements working together--as it should it be--the score can definitely be enjoyed on a casual basis outside of the game.
My favorite picks of the soundtrack are: Icarus, Hengsha Daylight (Part 1), Main Menu, The Mole, Singapore Ambient (Part 2), After the Crash, Penthouse, Namir (Trailer Edit), Opening Credits, Everybody Lies, Endings, Home and LIMB. I do enjoy the "Shanghai LIMB"(which wasn't included) more-so than the "Detroit LIMB"(which is still a great ambient track) only because It adds a little more to the song with additional instruments, but it's just personal opinion. The soundtrack doesn't suffer at all without its inclusion. Virtually every track in the game I would have included has been included, so job well done to Michael.
One thing to mention involving a few of the tracks; The Mole, Singapore Ambient, and After the Crash, come to mind. Some catchy electronic cues show up and are definitely worth a listen. I know some people may get bored of the slow pace in the beginning of a few of these tracks and skip over them but give them about a minute, you should really enjoy them. They ended up being some of my favorite tracks.
McCann did an excellent job for his second video game composition(Splinter Cell - Double Agent being his first). He set out to create a hybrid of ambient, electronic and acoustics to compliment the immersive open-ended world of Deus Ex, without becoming too abrasive or repetitive. While still managing to create melodies that are a joy to listen to. There were certainly a ton of great video game ost's last year--I could name about a dozen of them--but I have to say, this one stands apart in terms of originality and was my personal favorite.