CyanCat47 said:
The game actually does tell you when the enemy is aware of your presence. If you're sneaking around and an enemy NPC sees or hears you they'll bark out a line (ex: "Who's there?"). If you duck behind cover and wait, the enemy will bark out another line after a moment (ex: "It must have been my imagination"), give up searching for you, and return to their patrol route. If during that moment after the initial bark you don't move and remain visible, that's when they'll spot you and open fire. Don't just stand out in the open, even if it's shadowy. Find something to hide in or behind. Your goal is to actually break the line of sight. When sneaking up to an enemy, assuming you don't have the Run Silent augmentation, always crouch-walk. If you run, they'll hear you. Even if you walk, they'll hear you (though you can get
much closer to them before they spot you than if you were running). Even if you botch stealth entirely and the enemy starts firing on you, if you manage to evade them and hide, they'll eventually give up pursuit and return to their patrol route (indicated by another bark like "We lost him.").
The taser doesn't
require two shots. If you sneak up behind a target and aim for their neck/head, it'll knock them out with one. The hitbox is wonky, but once you get used to it you'll be able to one-hit pretty much anyone with the taser, assuming they aren't alerted. Alerted enemies generally take 2 or 3 shots. Some pretty specific enemies take even more than that, even if they're not alerted... and others still are immune. You'll recognize those ones when you encounter them. Its ammunition is actually relatively common in the early game too, if you explore (there are a bunch of them hidden throughout Battery Park and Hell's Kitchen after you leave Liberty Island). Its ammunition tends to be easier to overlook than other weapons because of the size/shape of the pickup. Many police, security guards, and UNATCO troopers carry it throughout the game as well.
Killing isn't heavily penalized. All it changes are a few lines of fairly inconsequential dialogue. Lethal vs. Non-Lethal doesn't have a whole lot of actual impact on the game's outcome or your available resources.
In addition to your handgun you can also choose to start with a GEP Gun, a Sniper Rifle, or a Crossbow. GEP Gun is probably your best bet, since you can find a Sniper Rifle and a Crossbow on Liberty Island. The Crossbow does add some additional stealth/non-lethal capability to your arsenal though with its Tranq Darts. There are multiple NSF troopers that carry Crossbows/Tranq Darts on Liberty Island, and there's a body on the ground outside of UNATCO HQ that has one in its inventory as well. It takes kind of a long time to actually knock out an enemy when your Pistols skill is low, though, so prepare to have alerted enemies chasing you for a few moments before falling unconscious. It's best to fire it, then duck behind cover and wait.
Stealth/Lethal, Stealth/Non-Lethal, and Guns-Blazing are all viable ways to play the game. Stealth in general is probably the most common way people play
Deus Ex. It just takes some time to learn the mechanics and level up the appropriate skills. The game starts you off weak, but that gets better as the game progresses. Once your Pistol skill is at Master you'll be able to instantly, silently take down most enemies non-lethally from a pretty good distance away with a Crossbow Tranq Dart to the head, and those darts are so common you'll be at or near capacity most of the time even with heavy use assuming you hit your targets.