Some of the biggest questions are still unanswered, and they are perhaps bigger than anything we have toyed with since the conception of the scientific method. We've just gotten tired of asking a lot of them and have accepted our ignorance. For instance, what is life? We don't even know in what branch of science this question belongs: social, neuro, biochemical, quantum, or something that transcends all that we can observe. We don't even know where gravity comes from. What about the notorious three-body problem? But besides all of this, I think the size of the discovery is measured by how much you care. I discovered something in my lab earlier this year that made me run home and kiss my wife. It was a big deal to me. We'll see what the peer reviewers have to say about it.
(Video courtesy of youtube and somebody else's copy of Spore creature creator)
I agree -- "What is life?" is a great example of an unanswered question that you don't need to be an Einstein to ask.
Thinking about this a little more, I'm guessing that "What is life?" doesn't fit clean disciplinary boundaries because it will someday be a discipline of its own. It's easy to forget that all the branches of science we take for granted today were discovered at a specific place and a specific time. The modern science of chemistry grew out of the pseudo-science of alchemy, largely thanks to the invention/discovery of the periodic table. Were those rows and columns the only way we could have grouped atoms and elements? Are atoms the only way we could have made sense of matter?
Since these ways of thinking are drilled into us from 3rd-grade on, it is literally "hard to imagine" a different, but equally true framework. And because the periodic table works well for a lot of things, we've given up looking for alternatives. But that doesn't mean that no alternatives exist. See The unreasonable effectiveness of mathematics for a really interesting discussion of this idea.
I'm convinced that the distinctions between scientific fields are invented, not inevitable. The whole truth is a lot more cohesive than our understanding of it.