I’ve said before that the thing a game is really about is the thing you spend your time doing. Doom is a game about shooting at monsters, The Ancient Art of War is a game about maintaining supply lines, and Riven, despite its best intentions, is largely a game about looking for animal shapes. Deus Ex — the way I’m playing it, at least — is a game about gaining access to things.
You can go about this in various ways. Often there’s more than one route to your immediate destination, with different obstacles, which use different character skills. For example, one route might have guards patrolling it, a test of your various weapon use skills, and, indirectly, your medicine skill, which affects how many hit points you can squeeze out of a health pack. Another route might have a locked door.
Sometimes you can find a key for a locked door. Sometimes there’s a keypad you can enter a combination into. Sometimes there isn’t. Mechanical locks can be picked, provided you have a lockpick, but these are single-use videogame lockpicks. I suppose this makes more sense in a dystopian cyberpunk environment than in most other milieus — after all, if the presumably-corrupt corporation that manufactures those lockpicks can make them self-destruct on use, they certainly have the financial motivation to make them that way. Similarly, electronic locks can be overcome with a disposable “multitool”, which, however, also has other uses (such as disabling security cameras). Doors and keypads all report strength ratings when selected. Supposedly the strength affects how many picks or tools you need to defeat them, but I haven’t yet seen a door that needs more than one, presumably because I’ve been sinking most of my skill points into Lockpicking and Electronics, which make the use of these tools more efficient. I do this because the supply of lockpicks and multitools is limited, and I’m afraid of running out when I really need one. I have yet to find a reliable source of either item; mostly I find them at random places throughout the levels, raising the question of who left them there and why they didn’t jealously hoard them like I do. Any mission that I finish with more lockpicks than I started is a good mission. When I chance upon a combination to a door that I already spent a multitool on, it’s time to reload an old save.
There’s one other way to open doors: explosives. This is also an effective way to deal with certain other obstacles, such as the aforementioned armed guards, but I haven’t been indulging much in explosions of any sort, because they tend to attract attention. Not all doors are vulnerable to explosives, just as not all doors can be picked or hacked: there’s a strength rating for how much physical damage they can withstand just like the one for resistance to being picked, and either rating can be “infinite”. I’m guessing that I’ll eventually start encountering doors that are infinitely strong in all respects, and can only be got past legitimately (with a key) or indirectly (through an air duct). There were doors like that in the tutorial, which was themed as a UNATCO training mission, and if UNATCO has access to infinite door technology, you can bet they’ll use it to guard their innermost secrets.