Serial Experiments Lain (SEL) is built around certain philosophical themes, such as existentialism. It also explores the Sci-Fi genre very well. The anime can be confusing for some viewers and make them get lost in the plot, since the world and character building isn't always straight and simple. But I do believe it is worth a try.
Story: SEL has Iwakura Lain, its protagonist, involved in multiple situations where the spectator can see how she reacts and acts upon them. From the first episode, the anime already intrigues you with some events and takes its time to explain them through the whole show.
Lain's universe is also very ahead of its time. The criticisms made within the anime are very into the future/today's world.
The philosophical aspects that build the show are also one of its best parts. Lain's perception and understanding of the real world and The Wired are very well explored and presented to us, making you question how do these two universes interact with each other.
Even though I did love the anime, I have to admit that sometimes it is hard to understand where it is trying to go. But for me, these moments are some of the most interesting parts because it does make you involve yourself with the plot.
Art: The artwork in the anime is very good. Personally, I haven't seen many shows from the 90's, but Lain did surprise me. First off, I thought it was a show from the 00's, considering the art style reminded me a little of Ergo Proxy (2006).
The anime creates some visual effects that perfectly fit the atmosphere created by the sounds (I'll talk about these shortly), some distorted and colorful moments.
The shadows are some of the most visually appealing parts of the anime's art. The colors that fill them and also the way they are used to construct the scenes' physical structures.
Both the intro and outro are also very well done aesthetically.
Sound: Outstanding. As written above, the sounds used in the anime create a very unique atmosphere that really puts you into the universe.
The anime opening ("Duvet" by BOA) is incredibly good and fits the show's thematic and aesthetics, both instrumentally and through the lyrics. The ending theme ("Tooi Sakebi" by Reichi Nakaido) also works.
BUT if you dislike electrical or computer noises as background sounds, it might be annoying to you.
Character: SEL's protagonist, Lain, is a very interesting character. She is well developed throughout the anime, almost every aspect of her personality and doubts are explained (except some parts left for the viewer to discover).
Alice Mizuki is a great friend that helps Lain explore and feel safe about the real world.
The rest of the cast do their respective interactions with Iwakura Lain to help the plot's development. Some of them have intriguing stories that you'll discover as you watch them.
Enjoyment: I really loved the anime and Iwakura Lain. I am very into shows that build an amazing atmosphere that you do feel like you were inside of it, props to the visuals and sounds.
But it does make you uncomfortable at times. The stories get heavy at some points, and some things are difficult to understand at first.
(If I stop to write about everything I liked, this will be very long, but I want it to be short and spoiler-free so yeah)
Overall: Serial Experiments Lain is a very interesting show that you probably should watch if you have the chance. The plot is intriguing and gets you involved with it from the start.
IF you are not into the Sci-Fi, Dementia and Psychological genres, noisy soundtracks, and non-straightforward/confusing at points plots then maybe watching SEL will not be entertaining for you.