Hyper Calvin vs. Orthodox Lutheran for example. Calvin vs. Armenian - Heck, Calvin vs. pretty much anybody.
Basically the idea of the elect taken to extreme.
There are other differences in who God is, who Christ is, but I think you'll recognize this one within Protestantism. If now, venture carefully onto the Tulip threads..
;)
There isn't a difference in who God is in those beliefs. There is a difference in what He does. But whether one is a Calvinist or not doesn't mean one isn't necessarily a Christian as it doesn't necessarily mean that one is not a Christian if they are Arminian in persuasion. They are secondary issues.