When humans find a new object or material or aspect of the world that behaves contrary to their expectations, it arrests our attention, and we poke at it to learn more. Primatologists use extended attention as a measure of "noticing something is strange" from chimps and babies - when something strange happens, they stare at it for longer. No doubt this explains the fascination with shiny nuggets in stream beds humans have exhibited for millennia, when we encountered the only metal to be commonly found in its unoxidized form in nature owing to its high redox potential.
It's this same pattern-recognition itch that motivates my, and I would guess most people's, investigation of consciousness. It's like diving into a lake and missing, every time. It is irredeemably strange that each of us encounters consciousness every waking moment and yet are at a loss to explain it coherently. It can be said that a rigorous understanding of consciousness would be the apex of the Enlightenment project, combining self-knowledge and how the universe works with a tool to alleviate suffering and the human condition.
It's useful to remind ourselves of what the big puzzles are from time to time. In investigating consciousness, I'm really most interested in the deep mystery of consciousness, also known as the sunset problem (why does the experience seem to be like something), or what Chalmers refers to as the hard problem. The mechanics of how pain, behavior, even free will (if it exists) arise are not that interesting compared to the deep question of how and why subjective experience exist at all. Saying that the brain produces consciousness (like Searle) does not eliminate the problem, and explaining it or its states away (like Dennett and the Churchlands) does not account for my own experience. I feel pain, and I desperately wish I could explain it away.
The most intractable aspects of the Hard Problem are outlined below.
1) Accessibility of experience. There is something it is like to be me, and I can never know whether there is something it like to be anything else. This is the first person vs third person barrier. It also seems to be something that can't be shared between conscious beings - we can never know if another is conscious. For all I know, everyone could be a zombie.
2) Consciousness seems to occur in some things but not others. Why? What are the prerequisites for subjective experience? Because of the zombie problem, can we ever answer this?
3) Consciousness seems conceivably separable from complex behavior. That is, there is no obvious reason why something would have to evolve actually having the experience of pain, instead of just being programmed to avoid pain. Is this a coincidence of life as it happened on Earth, a side effect so to speak? Or does consciousness play some necessary part?
4) Cognitive difficulties with discussion. Try to answer the question "What is consciousness?" We have an innate difficulty in discussing the topic, whether this comes from a lack of terminology or some twist of our nervous system that obscures the matter. Very bright and earnest individuals have trouble even understanding each other's basic definitions. We can't discount the possibility here that our problems in understanding consciousness result from our making assumptions that are so profound that we aren't yet aware of them.
5) There is no conservation principle in consciousness. This is a less discussed point, and may not even be that interesting. Still, it is a property of consciousness that makes it unlike other phenomena. In contemplating this point, I understand what is most likely the second most popular reason to believe in an afterlife: it seems counterintuitive that all this sensation I am experiencing could suddenly cease due to a simple collapse of chemical gradients, without violating some balance in the universe. Note that I am emphatically not arguing for any spiritual interpretation here - but this seeming paradox could be useful in learning more about consciousness, and it is undoubtedly part of what encourages humans to believe (incorrectly) in some life separate from the physical.
Consciousness and how it got to be that way