Is there anyone where who believe on the God that is mentioned in the First Testament? The guy who commands people to slay 7 nations, including women and children? The guy who mostley talks about punishment and not about forgivness? Where no devil even is mentioned, only the God who can be evil and good, depending on how faithfull people is? But somehow he seems to prefer killing people in that book.

Most people probably believe in the God that is mentioned in the new testament. That's a kind God. But whatch out, there is a devil, somekind of evil "twin" to the God who tries to fill people with lies and make them do evil stuff.

Well, there are severals Death Metal bands who are christians who believe in the first-testament-god. A God that doesn't show mercy to the unfaithfull and is somehow a little chaotic: "the power I've given, I can take aswell"/John Shaffer (That's the devil speaking to Spawn, but's the same principle). He can create, destroy, erase and revive (DB) as he please.

No, people should believe in whatever they want I guess, and I don't think there is anyone who have the same belief as anyone else. Everyone has there own model or system of how their God/Gods thinks and acts..