Watching Steins;Gate, all I can say is that the following comment by Talha Ashraf (when I had asked him about Serial Experiments Lain) was so right.
looking at the cover for this [Serial Experiments Lain] anime, hell no!
You know I've seen sad movies but the thing with dark animes is that the word sad does not cover it. They're on a whole different level. A dark anime will reach into your chest, squish your heart, pull it out, put it through a meat mincer, twice, and then put it back in its place while you try to grasp what happened.
There couldn't have been a more apt description.
Funnily, Serial Experiments Lain wasn't that dark. In a sense, you can say, it kind of was. But not in that way.