Shortnote
Deus Ex: Human Revolution is an exhaustive, albeit tedious, game if you like sneaking around and taking out enemies silently. One of the most dreaded parts of the game are the bosses, that have been a source of complaint from many gamers. The reason is that, while playing on a sneak run and trying to subdue enemies without killing them, you end up face-to-face with a boss that packs a lot of damage and, due to very small inventory space, you are never prepared to handle the battle.
The following chart presents an augmentation tree that was captured at the end of the game with callouts and colors indicating how useful various augmentations are. Please expand the picture for a larger version.
The following notes can be made for the various augments that you can choose:
The Typhoon attack system is the best way to kill any boss in the game with just a key-press. If you are tired of bosses, you can invest just three points in this tree and every boss can then be killed with one or two discharges of your Typhoon system. This is the most rewarding and painless way to get those annoying bosses out of the way.
Second on the list is the ability to hack higher level devices - this is not really an upgrade since it just allows you to start the hacking mini-game. The other hacking abilities are not really needed since you will slowly get an extreme proficiency in either looking up passwords and codes or playing the hacking mini-game on very many occasions. Nevertheless, the game is built around keypad and passworded computers and a lot of content can be revealed if you have access to these devices.
The yellow colored shout-outs are nearly essential. For example, the arm augmentation that just allows you to lift heavy objects, will allow you to reveal hidden path-ways and get around in the game more easily. The same goes for the leg augment that allows you to jump (what they call) 3 meters since the jump distance is ridiculous in the game. The Icarus landing system saves you very many problems and generally speeds up the game - however, you will rarely use the Icarus while on a mission and sneaking.
There are two types of environmental damage in the game that you can become immune to: gas and electricity. The augment that renders you immune to gas is not really necessary - although you do meet a boss that uses gas grenades toward the end. However, the gas environment during missions can be bypassed by either turning off valves or simply choosing another way without any penalty to your sneaking desires. On the other hand, electricity environments are very common. In fact, in the last movement, you meet a level that a whole basement full of dangling electric wires which are (conveniently) hooked up to the floor. Same-wise, towards the end of the game you are required to infiltrate some docks and the only apparent way in is either guns-blazing through the front door or by jumping on top of some containers that are (again conveniently) hooked up to electricity. Thus, between gas or electricity, if you want to save up augments, go for the electricity upgrade since it will be essential.
Conclusions
One of the funniest things about games that allow you to sneak around and down enemies silently, is that you can waste a lot of time, doing your best not to kill anybody, when your sneak actions do not really influence the outcome of the game. In fact, Deus Ex: Human Revolution leaves you with an empty feeling if you have been sneaking your way around. As you can see from the image above, there are still 12 unused praxis kits due to careful planning and saving up points that could be useful later.
The general recommendation, is that you will have much more fun if on several occasions you just go in with guns blazing. The result of doing that, similar to Betsheda's Dishonored game, is just the wording on the end-movie. After all, if you were planning to play the game, you most likely bit and have already seen the YouTube videos for the different endings.