They were both similar to me in that Shinji realizes that his state of happiness and general being is entirely up to him and how he chooses to see things in his own mind. Obviously both endings are different when you take in to account the events that happened in each one, but at the end of the day it's all about Shinji and how he chooses to look at himself and his place in the world he lives in. Hell, the entire series almost revolved around Shinji trying to sort his bitch-ass, angst ridden self out.
I was under the impression that EOE took place because 99% of the moronic EVA fans wanted rock 'em sock 'em EVA on Angel, Asuka on Misato action, therefore moving Hideaki, or whatever his name is, to "murder" the characters in a gruesome way so as to spite the fanboy-ism surrounding the series, yet still carry out the story of Shinji's self-realization which, as far as I'm concerned, is the most important theme of the series...