Some Geth wrote...
"They are great for people who are new to anime."
Ghost in the Shell is great, but um.. I think it helps if you have some anime, good anime experience first. Same with Ergo Proxy.
Fair enough if that's your opinion, though mine differs significantly:
Both GitS, the GitS:Innocence and finally the series GitS:SAC are simply anime, as good a starting point as any other. The only thing that makes them different is the discussion those anime tangle with and the scale thereof. And whilst I could agree that someone that has no idea about what GitS is playing with, the philosophical discussion about the essence of a being, the question of what makes one human, mind or body or the connection of those two, experience or information and to what experience is compared to information, the social criticism and the rather obscure social mechanic of a stand-alone complex (that's a real mind**** by the way, still haven't figured that one out completely!) might not really value the anime's intention of dealing with it and its execution, but still the show has plenty of eyegasm, eargasm and action to satisfy more superficial attention.
And Ergo Proxy is something special anyway. If you like mind****, Ergo Proxy is THE anime to watch, and it's sci-fi setting. Not easy diet, yes, but quite enjoyable anyway.