Good question, not too wide, not too specific in my opinion.
Maybe this is the place to give a definition to consciousness first of all. Conscious means a state of being aware, which comes from the Latin base word scire (sciō) meaning "to know" or "knowledge". Other derived words from scire are science and conscience. On the other side Greek counterpart for the verb "to know" is gnosis, which has a very probable root on Sanskrit word jnana (gñāna). I'm lifting this up to show that traced meaning of the word we use here has a pretty mystical background. And perhaps by this reason, we give consciousness a very mysterious meaning, like a magic soup that is flowing in us, our brains or in the world around us. I'd like to take a different point and view the mystery of the word coming partly from the "everlasting and doomed" efforts to define something that has no clear objective by limited and mixed words AND stubborn way we want to maintain the mystery for the word. Mystery itself is kept because of three reasons:
we experience ourselves as a self-conscious persons (strong)
religious and cultural teachings coming from the environment
where we live in (medium)
philosophical discussions about definitions that becomes
pointless by the nature of logic based on language (weak)
I will go little deeper only to the first point. 2nd is the burden we get away pretty easily by education and 3rd is not so important thou it could raise a whole new topic to explain and prove what I mean with it.
First case relates to mind, soul, Spirit and awareness topic. Until it is empirically proved that conscious exists outside of the person (brains) itself, there are no reasons assume otherwise. Its true there are a lot of stories in west (mediums, clairvoyance, OBE, afterlife experiences and so forth) and east (sadhus and yogis, meditation and monks) that gives interesting material for research, plus modern theories on quantum field gives new dimensions, but we still stick on open questions. No definite proofs has been provided that soul, spirit, mind or consciousness exists but in our body only.
I say in our body, because I cannot deny that we experience consciousness, being aware of self (I am) nevertheless. Explanation for this comes from purely biological perspective. Sensory (five senses) system attached to a complicated electro-chemical neural network memory called brains gives an illusion of self-awareness by recursive and predictive signal transmission.
Inner talk, imagining, day and night dreams, all are reflections of memory signaling back and forward on brain and sensory system interface. This is nicely explained on Jeff Hawkins's On Intelligence book, chapter 7 "Consciousness and Creativity". Topic is blogged on: http://brianandrewsauthor.com/2012/02/08/on-intelligence/ for example. In a way western and eastern mystics, that say the world and (some dare even to say) also the very self itself is Maya (illusion), are correct. They may add some other extensions to the fact, like oneness and bliss that can be experienced in spite of Maya. But they are not really proof of conscious being other than single mind product in a single person body.
Now from this point of view answer to your question is: the characteristics of consciousness are subjective, memory dependant, temporal and changing, illusive, yet developing to some extend we don't really know yet.
And yes, the word consciousness is very fundamental and practical to discuss on topic like this. It would be almost impossible to replace it with other descriptive word and still maintain focus and be understandable.