I'd definitely have to say Neon Genesis Evangelion. Probably one of the most psychologically devastating and harsh series I have ever seen. I don't know why but I guess it opened me to so much more in life and really got me thinking in a much more critical way. I'd say that series alone destroyed what childishness I had left in me. Though I'd have to say it also probably tormented me for the next few months :>
I guess a plus was using the soundtrack while studying for my final year exams, and then before I would walk into the exams I would play a certain song and it'd all just bring it back to me. Fair to say, I got A's and A+'s in all of them. So it did well for me.