One defining characteristic, for most people and religions, would be 'Creator of the Universe.'
Exceptions? For some Gnostics, this particular physical construction we dwell in was evil -- at best a mistake, a lapse akin to playing with mud pies, something only an inferior deity could have perpetrated. That necessitated a 'Real God' in a higher, more spiritual reality: either God seen as the creator of lessor spirits, or as the one from whom they just emanated -- at the least their ultimate superior in power and character.
A common flavor in many religions paints this world as a place of suffering or futility, which we do best to escape from, no matter its origin. I've got to agree with the Jewish tradition that God made it and called it 'good', that God could at least say that about the original product.
There isn't much point trying to argue that with anyone who's finding this a bad place, aside from the obvious fact that most people, most of the time, don't actually kill themselves. People find some beauty (we're told) even in utterly ghastly situations. We want to know how it comes out, we want all we can get of this life -- or we realize on some level that we don't have the actual power 'to be or not to be'. We're in this thing called Life and had better deal with it.
However you decide that one, the world is the first, most pressing evidence we get as to what God is like. That isn't so much the abstract things we know about science and history and the current condition of the world -- but what we experience of living. Not so bad, not so good... but then we find, if we're lucky, that Something less obvious is at work in all that, is seeking to get our attention.
Some of us are more lucky in that sense; this isn't fair! And so it isn't, on that level. This follows from the inferred, observed fact that God isn't easy to get to know!
Some people insist that God isn't in fact knowable, that any divinity we can know must be some lesser being. That's a convenient view: gives us a lovely conception to contemplate while kicking any immanent version of God safely upstairs. It may even be true; but it's moot. All that we can know is the One who's striving to be known. And that One is elusive by Hsr very nature, and by our very nature, and that tricky relation between us.
There's this physiological thing called 'the blind spot.' Every human eye has one; there are techniques you can use to 'see' that it's there (although of course you never see anything there; that's why it's called a blind spot.)
Of the two most logical ways to design an eyeball, our eyes grow in one form while a squid's eyes grow in the other. You can have 'retina inside, nerves outside,' -- or you could potentially have, like a squid, 'retina outside, nerves inside.' Our human version is a design flaw... but it does provide a useful metaphor. In the very place where we have the most retinal neurons, where all these little fibers are coming together to plug into our brains, there is no room for the light-sensitive rods & cones. That's our blind spot, right in the structural center of what we see by.
God is hard to see because God is what we 'am' by.
Elijah found that God was not in the fire he saw, nor in the strong wind, nor in the earthquake, but in a quiet 'voice' inside. That's the best place to 'look'.
Where is this "inside"? In our heads, in our hearts -- our tummies? If you must have a physical location, there seem to be many possible starting points -- but if you consider the real place to be in the very 'looking' you're looking with, you get a hint of what makes for that 'elusive' quality!
Is this another 'convenient' view? -- Does it place 'God' safely inside where He can't get out to make trouble? Some people think so, find it so -- but if you keep on meditating, that pesky 'inside-vs-outside' distinction gets problematical.
Does this view make us God? Won't it tempt us to run around loose imposing our Divine Whim on everything & everyone? Well, consider what the word 'you' means. There certainly are a great many things going on in your head -- and your heart and various other places -- that may not entirely represent your best self, what you truly (eventually, if it isn't so very much trouble) want to do. All of it is you. All of it is a manifestation of God's ongoing life living you. Everything you did as a baby wasn't charming, nor is everything you've been doing since; but the process is life; and it grows in wisdom and in stature. (With some setbacks, sure. But what you 'are' is eternal.)
So God is striving to be known, and need not be in a rush about it. What about us? How urgent is our need? That sounds like the subject of another post.