Let me add that if you liked Serial Experiments Lain, you might want to check out Haibane Renmei and Niea under 7, both by the creator of Lain. Very different subject matter though.

Generally if a series gets me to watch multiple times, it's pretty good. Once you've seen more super robot and mecha stuff, I'd recommend Kidou Senkan Nadesico (Martian Successor Nadesico is the US title,) which I have re-watched at least 8 times over the past 10 years.