Sorry about the bluntness of the following post, but I thought I had to express my take as clearly as possible to resolve our difference of oppinion. If you think I'm wrong, be sure to point out where and how.
The rebreather is better than aqualung which is better than the swimming skill.
I've already argued why that's not necessarily the case, but I'll try again since you don't seem to address that part. Rebreathers require additional exploration and inventory room, and sometimes backtracking. For a veteran who knows exactly where all the rebreathers are and know how to houseclean their inventory, maybe you're right, but you're never designing the game for the veterans. Furthermore, you generally don't know whether or not rebreathers/backtracking is even viable when you make the investment, not to mention, you don't really know it as you're exploring.
From the perspective of a new player, as a result, you're wrong. One option is not strictly better than eachother.
But the fact you can circumvent that choice very easily by just carrying a rebreather or the aqualung aug negates that choice.
Just argued that the premise for this is false, so if I'm right about that, this is by extension also false. And again, you could rebalance it.
Now, if the systems were balanced, for example if the rebreather took up a load of space (somehow), that would be better. But that would add needless complexity which makes you focus more on the system more than the choices.
Excuse me, but what are you on about? In Deus Ex, you can sometimes either multitool, lockpick, break in with melee, break in with sniper, break in with minicrossbow, break in with explosives from your inventory, break in with explosives from the environment, hack, or discover a password, to gain entrance into something.
What choices are available to you depend on your build and the situation, but you nearly always have multiple options with multiple costs. You choose which resources to exhaust, or maybe you even leave it alone because you don't think it'll be worth it.
This is exactly the same thing. You have many resources that allow you to traverse a specific part of the level. Some require skill investment, other require augmentation investment, some require inventory items, some require exploration. If you want to cut the manners by which you can traverse a specific part of the level underwater because it adds needless complexity (what does that even mean? When is complexity meaningless and why is this complexity meaningless?), why would you not also want to cut the manners by which you can traverse any given doorway?
I mean, look, swimming isn't an interesting skill, taking it has no side effects other than letting you traverse specific parts of a level, so at present it's a fairly _boring_ skill, and it might well be unbalanced in that the choice between taking it or not might be too simple. But dude, no, it's not broken in the fashion you depict it, and it's not anywhere near as fundamentally superflous as you seem to suggest. You're wrong about that.
If you like that kind of game, fine, but that clearly wasn't concept behind Deus Ex.
Oh yes, yes it was. The concept was, the player needs to have many ways to do the same things in any given situation, and those ways will be available to him based on how he build his character and what items he picked up and where he explored, and they will have distinct costs associated with their use that are different from option to option.
There's an absolute truckload of overlapping systems letting you do the same basic things, but they each have different side effects and costs.
Also, just to make it clear, I wouldn't call it the concept behind the game, those are the words you used to make your point. I used the words in the context you used them to illustrate as firmly as I could that you're wrong about the point you were making. I would describe this behaviour not as the concept behind the game (which would clearly be something more abstract), but rather as a fundamental tool used to make the game what it is.
Having multiple systems doing the same thing doesn't increase the amount of 'dynamic situations', it just means more time spent in menus and fussing with character management than playing the game. That was my point, not anything about 'dynamic situations'.
Also wrong. Having multiple systems with multiple costs of entry and cost of use means that the player has to think about how to best apply his resources to solve any given problem. The LAW is the perfect illustration: A one-use gun that can take down a single target, but afterwards the gun is spent. If you generally don't use guns at all, and don't want to use skill points or room for heavy weapons, then it's a perfectly viable alternative. In this case, you solve the problem posed by one particular enemy by using your inventory space, rather than sneaking, hacking, or a general choice of heavy weapons or explosives.
And that's just it: The overlapping systems are really overlapping solutions, and what they present as to the player is dynamic situations. The fact that you have multiple ways of taking down heavy targets doesn't make the player fuss with character management, it makes the player feel empowered, and responsible for his own position in the game. As such, it is absolute key to the success of Deus Ex' gameplay that you have meaningful, assymetric alternatives.