If God (using the memtic definition of inspiritaion, the holy book of choice, and the word of followers) says that he exists, loves us, and will damn us to hell, he’s lying about something. Therefore, He could be lying about everything else, too.
—It’s not that God says he’s omniscient, it’s that omniscience is simply part of the definition of God. (Assuming we’re talking about the Judeo-Christian conception here.)—
I think you’ve missed the whole problem. Yes, you can play with definitions: but you can’t necessarily demonstrate that the definition has anything to do with what you’re talking about. That’s a bait and switch tactic. There may be a god, and that god may say it’s omniscient (whatever THAT really means), but we have absolutely no way of evaluating the truth of that claim, especially if god is at least a great deal more “scient” than we are. Indeed, we have no way to evaluate the truth or falsity of anything about a god who is apparently beyond our understanding.
Indeed, as some people point out, omniscience at best only makes sense with regard to external knowledge: full self-knowledge seems to be incoherent.
At the very least, god could simply be sincerely wrong about his own omniscience. How would he know if he was, if that knowledge too is something he doesn’t know (and doesn’t know he doesn’t know… and so on)?
—If God exists (and I don’t think he does) then he pretty much gets to decide what’s moral.—
No. This concept, of “deciding” what is and is not moral, is incoherent. If it were true, then we could not really be talking about what we all think of as being morality.