I think Eva is fundamentally about one thing which is dealing with the pain which is fundamental to human connection, and whether or not it is worth it. If you had the choice to shut yourself out from others completely, thus eliminating the inherent pain/conflict of human interaction, would you? Should you? Or, alternatively, if you could alleviate this pain by eliminating individuality completely, blurring the lines between you and everyone else, would you or should you do that as well?

Any other theme you might be able to identify ultimately stems from this question. What is the big argument against the dissolution of human boundaries? Well, one would lose their sense of self. Losing one's self would be terrible if one loved onesself. But since this person doesn't, everything would be so much easier if the boundaries between us and others just slipped away. Complete acceptance and no resistance.

But once that happens, what do you lose? Can it ever be worth it?

Which is why self-love or valuing ones self becomes so important. How can one be expected to value human individuality when ones own individuality is at best always painful, or at worst, inflicting pain on those you love?

Once you become so deathly afraid of hurting others and being hurt by others, your options are either complete isolation, or in the world of Eva, the dissolution of every boundary between humans. Which, of course, is not an option we have in reality.

If you have never struggled with this, if you have never wanted to stop existing, if you have never wanted so badly to stop hurting others that you would do anything, if you have never feared that we would all be better off dead or alone with no capacity to hurt anyone, etc, then I don't see Eva resonating that strongly with you. Or, as you pointed out, if maybe you used to think about those things but now you've found yourself on the other side, perhaps you would have fallen for Eva back in the day.

As for the other two themes you mentioned, the cycle of life and death, and "change is the only constant," I don't know if I really buy the relevance of those at all. Cycles in general perhaps. But I'd be really curious to hear an argument on behalf of those themes. I don't see them being very important to the show. Interesting that you say you felt it was straight-forward because I don't really agree with your read that much.