If you liked
Narutaru: Mukuro Naru Hoshi Tama Taru Ko
|
...then you might like
Alien 9
|
Cute shoujo at first? Check. Mons? Check. Coming of age story? Check. Half-finished anime? Check. Incredibly, incredibly disturbing? Check.
If you liked
Serial Experiments Lain
|
...then you might like
Key the Metal Idol
|
Serial Experiments Lain is the (improved) spiritual successor of Key the Metal Idol. Expect similar themes and storytelling devices.
If you liked
Serial Experiments Lain
|
...then you might like
Boogiepop wa Warawanai
|
Total mind screw. Serial Experiments Lain is more understandable and has a (sympathetic and well developed) main character, while Boogiepop Phantom is more confusing and creepier.
If you liked
Narutaru: Mukuro Naru Hoshi Tama Taru Ko
|
...then you might like
School Days
|
Narutaru is the only show I've ever seen that's more depressing than School Days (not sad, neither show is sad). Both appear cheerful for a little while before getting worse.
If you liked
Shinseiki Evangelion
|
...then you might like
Serial Experiments Lain
|
Dark, psychological, philosophical, mysterious, Lain and Evangelion are very similar thematically and tonally. If you like one (or if you didn't absolutely hate the last two episodes of Evangelion), you'll almost certainly like the other.
If you liked
Shinseiki Evangelion
|
...then you might like
RahXephon
|
They share a ridiculous number of specific and general similarities. Essentially, RahXephon is a much lighter and brighter version of Evangelion. Evangelion has significantly more psychological and philosophical elements than RahXephon, but RahXephon sounds and looks far better (also is less screwy, if you're not a fan of mind screw). Either way, if you like Evangelion, you'll definitely like RahXephon.
If you liked
Saishuu Heiki Kanojo
|
...then you might like
School Days
|
Depressing as hell. Also, both romances that look like they'll be cheerful and fun for about five minutes (SaiKano) or three episodes (School Days).
If you liked
Gunslinger Girl
|
...then you might like
Saishuu Heiki Kanojo
|
Both about girls who are in the wrong place at the wrong time and are turned into weapons of war. They are very similar in tone, and focus on some of the same themes, though SaiKano focuses more on the costs of fighting rather than the costs of being turned into a tool for fighting.
If you liked
Mousou Dairinin
|
...then you might like
Serial Experiments Lain
|
Both are heavily psychological and philosophical (Lain is more philosophical than Paranoia Agent) with mysterious circumstances and great characters (or for Lain, character).