even though it was already shown to be an alternate reality

"Hey Gimmy, take the keys to the Gurren-Lagann. I hope you get about as much action as I did in there!http://spcows.ae2t.net/kareha/src/1185589895566.gif"

So that first episode was about what'd happen if Simon abused his powers? Or rather if he just kept on as leader? Didn't he say he'd see to it himself that the Spiral Nemesis would not occur? Why did he resign himself from the world and seemingly abandon all responsibilities?

Throughout the series they were just emphasizing how if you believe in yourself and try hard, you can achieve anything, even the impossible.. Yet here is Simon giving up and becoming a wandering "nobody" at the end... Is it right to show this kind of ending, of somebody breaking and giving up in life, after such high spirits throughout the series? It was all about overcoming life's obstacles, and it seems that it ended with Simon unable to come to terms with this last one...

It just leaves a bitter taste in my mouth to think that somebody like Simon became so resigned and insignificant after all that he had done for the world. If it was to show he was sacrificing himself to prevent the Spiral Nemesis, it did so in the most sad and discouraging way I can imagine.

You're getting it completely wrong. It's clearly shown that Simon isn't "giving up," he's resigning himself to the position he knows where he belongs.

He says "I'm a driller," meaning he will lead only to create the path, but when the time comes, will stop being the leader to allow those who are more suited lead. It's the exact opposite of not coming to terms , it is coming to terms with who he really is. Sure, he may not get the fame and fortune we'd like to see him get, but it's clearly not what he really wanted. He wanted to stand up when it was necessary, and then back down.

I think the problem is, people aren't thinking about the ending seriously, something I can understand. I mean, you have this mostly non-serious show, with an ending that is deeper than most of the entire show, so it's easy to just see the ending as what it is, rather than what it's supposed to be.

Like all good stories, there could be multiple interpretations to the ending. My view was that Simon had been fighting to go to the heavens all his life - "fighting his destiny", as it were, fighting from being trapped underground. It was all about non-stop progress, going higher and higher - piercing not only the heavens but space time and beyond... unstoppable progress like evolution itself, the basis of Spiral Power. And he did achieve what he set out to do, sundering the heavens and dimensions and all to create a new future for everybody. But in the end he returned to what he started as... a nameless driller. Kind of sad and ironic, no? It went against the entire image of him displayed before - a drill that pierces the heavens, not one content to remain a nobody underground.

Thus my theory was that he became like he was to prevent the Spiral Nemesis.... Because if he had kept going the way he had, using spiral power recklessly, it would lead to destruction of the universe. That's my interpretation of his actions, and I'm still a bit sad - but it makes sense if I think about it that way.