This game is... interesting. So interesting, in fact, that I would recomend playing the original game, skipping this title completely, and then playing Human Revolution. Anyway, if you care about my opinion, read on! Otherwise, I hope you have a nice day anyway.
As far as ambiance goes it is reminiscent of the original game. The dark and oppressive cityscape, the futuristic techno music, the neo-noir use of shadows and, of course, the color blue.
The one improvement this game has over it's predecesor is the ragdoll mechanic. Stuffing the limp bodies of victims into the ventillation grates is more entertaining than the story itself.
This, of course, leads into the story. I played this game for about five and a half hours. In that amount of time in the first game, I stopped numerous political terrorist plots, took out some nasty drug dealers, saved a girl from a pimp and many, many other things. I definitely felt like I was making a positive difference in the world.
In the first five hours of this game, I escaped from a bizarre super-soldier training prison that was under attack from generic religous terrorists and then wandered around for a while fighting mercenaries, killing random gang members, discovering the the terrorists were purposefully religously generic, cheated in some illeagel gambling, burglarized some rich dude's apartment, and wrecked a coffee shop. I felt like a roving psychopath.
In the first game, I felt torn between the urgency of completing the story missions and helping people by completing the side quests.
In this game I felt like there was something I was supposed to be doing, but I had no idea what that thing was or if it even mattered.
The first game eventually gives you a sense of moral ambiguity; over time you learn more and more about all the factions competing with each other and learn that every side does varying amounts of honorable as well as evil actions. Aligning with a certain side doesn't make you feel any better than the other side, but you just feel like you need to go with the lesser evil in order to save humanity.
This game gives you an immediate feeling of moral ambivolence. You discover within the first thirty minutes that every faction you've encountered has a mixture of good and bad intentions which culminate in stupidity. There is no urgency. These people are just going to fight amongst each other for ambiguous reasons and they want to draw you into it all. At that point I figured I'd just go and see if there was anything remotely interesting happening elsewhere. Cheat in some underground mutant lizard fighting betting? Why not. Get involved in a feud between rival coffee chains? Sure! It's more interesting than helping the Orwellian police force fight some self righteous murderers.
Last and perhaps least, we have the player character. In the first game, you get to be the badass JC. Do you think his baggy coat is unnecessary and it's ridiculous that he wears sunglasses at night? He could not care less about your opinion. If you order him to do something he thinks is questionable, he will not blindly follow your orders. He will do what he thinks is right, and he will go about it however he wants. Playing as him, you feel like an awesome futuristic warrior as you gradually upgrade his nanotech and acquire new and better equipment.
In this game, you are Alex. His/her character was not developed at all in the time that I played. All in all, (s)he pretty much just lets the different factions tell him/her what to do with very little (if any) question or objection. Truely, a compelling character. Playing as this wimp, you get a bunch of weapons and upgrades almost immediately and not much of anything to do with them.
This game is not technically good. It is not even that fun. As an experience, it's a mediocre spiral into the depths of a deranged world. The prequel is amazing, and the first game is a masterpiece. This sequel is ultimately disappointing. It is basically just one of the many Godfather 3's of the game industry.
This is all, of course, just my opinion and I sincerely thank you for reading it. I hope it was helpful. Have a nice day!