What school of ethics do you identify with? I think the best ethical theory is hedonistic altruism, or the view that the sole objective of moral behavior should be to increase the happiness/minimize the distress of other sentient beings. In my view, happiness/suffering is the only 'thing' that makes the world good/bad, it's the only thing that is inherently good/bad for it's own sake. The things that cause happiness and suffering are only instrumentally good and bad on the basis they cause happiness and suffering. In a world without sentient beings, it seems obvious to me that nothing would 'matter' since there would be no one who could be emotionally affected by anything.
It's hard to simplify yourself with just one ethical philosophy. I personally see myself as a mixture of secular humanist and existentialist with a hint of nihilism. We derive our meaning and purpose and reason based on what we claim to be true, yet there are things we have to consider that are factual by universal means as to how the world works without the auspices of a higher entity. Regarding ethical behavior, I feel life is just an experience. And as part of that experience we simply make the best of the best of times and the worst of times.
