A decent tribute to the original
Deus Ex: Human Revolution makes a good effort at recapturing a lot of the things that made the original great. The levels are filled with alternatives routes you can take, air ducts, doors you have to hack and all that stuff you are familiar with from the original. There is also tons and tons of sneaking around and city hubs where you can walk around and solve plenty of side quests. At around ~25h the game is also of a good decent length.
That said, Human Revolution falls flat at actually evolving the game in any meaningful way. The levels, while still rather open compared to other shooter, don't really feel any more open then in the first game. City hubs, while a little bigger then other levels in the game, still have the usual corridor-feel to them. The whole level construction of game still lacks any real feeling of authenticity, a lot of the air ducts make no sense other then providing a way to get from one room to the next and the amount of email that goes around telling you about passwords is still ridiculous.
The games story is a let down, while the marketing campaign made it look kind of insightful, the actual game rarely deals with the human augmentation aspect in any meaningful way, instead it's used as a cheap MacGuffin so the terrorist have something to fight against and the big corporations have something to make money from. The game essentially completely fails at establishing any interesting characters. All the people you meat on side quests never integrate with the bigger plot and the bigger plot is controlled only by a very small number of rather uninteresting cardboard cutouts.
The RPG stats in the game have been scaled back a lot, while there are still upgrades you can get by investing points, they are mostly focused on giving you new abilities, not on improving existing abilities. The lack of any meaningful upgrades when it comes to weapons, you can carry anything you find right from the start, also means that sneaking is really the only proper way to play the game. And you get so much points that at the end of the game you will have upgraded almost everything anyway.
The games balance also feels a little odd. You can die in the game really quickly, two or three hits and you are dead, which makes taking cover a must, but on the other side the enemies feel extremely weak as well. They have no real AI worth to speak about, other then taking cover and they can be put out of action permanently with a single hit of a stun gun or melee attack, even the bigger ones. The only exception are the robots, but they are rare and even they won't last long against an EMP grenade. So while you will die a lot, you will never have much of a hard time taking down an enemy.
As the game progresses there is also a noticeable shift from sneaking to shooting, which wouldn't be much of an issue if you could properly prepare yourself, but shops to buy guns and ammo are rare and ammo drops from enemies are completely useless, as they generally will provide you with only two or three bullets, while you might need 20 to kill them when you don't go for a head shot. So while I never got into real ammo issues, thanks to upgrading my inventory early on, I did have to throw away my upgraded sniper rifle at one point as it has become useless due to a lack of ammunition.
On the technical side of things like game is a little mixed. The graphics look for most ok, but especially the NPCs often look a little unpolished and their heads also look unnaturally small. The biggest problem is however the performance in the city hubs, those environment are extremely heavy on the CPU, far more demanding then anything else in the game. This meant for me that I could run around most of the game perfectly fluid (Intel Core Duo E6300) and then in the city hubs it would go down to like one frame per second, absolutely unplayable. It's not a game breaker as the city hubs don't have any combat and since one can work around the issue by looking to the ground or at a wall, but it certainly shows a lack of polish.
There are also some other minor issues, load/save could be a little faster given how often it's used in the game. The idiotic limit to 99 saves is annoying. The video tutorials at the start of the game are absolutely awful and completely break the flow of the game, they feel like an afterthought. The second boss got stuck in a wall so I could defeat it without any resistance. Dialog skipping doesn't work per line, but per whole dialog sequence of a character, meaning you can't fast-read through dialog. There is no NewGame+, which given the flat RPG stats however isn't much of a loss.
So overall it's a bit of a mixed bag. I did enjoy the game overall quite a bit, as it's a kind of game you don't see very often these days, but it's not really what I would call a worthy successor, more like a nice tribute. It's not as good as the original and not quite as much fun as Alpha Protocol, which used many of the same mechanics, but provided a dynamic storyline, meaningful upgrades and far more interesting characters. While the game mechanics and balancing certainly have some issues in Deus Ex: Human Revolution, I think the biggest problem with it is in the end the lack of likable characters. After 20 hours of helping random side quest guy I found myself just skipping through much of the dialog, as none of the side quests really integrate into the larger story and the stories themselves are not that interesting, especially as you never see any of those people again after helping them. Most of the email and text you get to read is even more uninteresting. In the end it's not any single specific thing that bugs me in Human Revolution, but that all the parts don't fit quite as smoothly together as they probably should.