I wish the developers of today had the guts to take on a project like Deus Ex
If a friendly character is killed in Deus Ex, it isn't game over. Life goes on, and the death of characters will affect some elements of how the plot plays out later on. And when a friendly character dies that you knew you could have saved it actually makes you feel guilty about letting them die.
In Deus Ex it is actually possible to run through the entire game without killing anyone! You can use tazers, asp batons and tranquiliser crossbow darts to knock enemies unconcious. Some people seem to get obsessed with not killing anyone, but I think it's best to strike a balance, as character Sam Carter will advise you.
If you know you can feasibly knock out an enemy without killing him, you should, because not only will you spare the poor guy's life, you will also incapacitate him without his letting out a blood curdling death-scream, alerting all around him to your act of homicide. However, if you intend to go through the entire game without killing a single person, it will get very monotonous and you will have to quick load often. Aside from that, some of the characters of Deus Ex are truly vile people and deserve to die. When you come up against the black uniform agents it is almost irresistable to kill them, since when they die their body self destructs in a satisfying shower of meat. Whether you play the pacifist or not becomes largely irrelivant later in the game anyway; there are no special awards for not killing anyone.
The plot of Deus Ex opens with a struggle between the anti terrorist force UNATCO and the terrorist group NSF as NSF have stolen several crates of the cure to a plague called the gray death. On one hand if they steal the cure it could wreak havok if the government in power dies of the disease, but is it right to withold the cure from all the ordinary people who are dying every day? You'll want to approach situations with an open mind. I won't give away any more of the plot since there is significant appeal in uncovering the story.
The AI of Deus Ex aren't extraordinarily combat apt as they will tend to run at you shooting most of the time, but they are devious in other ways. Enemies will often run to hit an alarm switch before engaging you directly, and if an enemy is badly wounded they will run away, bleeding all over the place! Sounds hilarious, but the poor fella usually isn't just running around like a headless chicken, no, he's run off to tell mummy. If you don't put him down one way or another you can usually be sure that a bunch of his mates will be come sprinting around the corner seconds later with your head in their sights. Even civilians aren't just cardboard cut outs. You can talk to them, and if they witness you attacking someone they will run and get the police.
All in all Deus Ex is a fantastic and unique game with a deep and interesting plot. Developers these days could really take a leaf out of Warren Spector's book; it is a shame that most devs just want to play it safe and not be too ambitious with their game concepts. The graphics are really of no concern. They serve their purpose, and I can honestly say that Deus Ex was much a more intriguing and fascinating game than most of the recent games I have played.