Not much. No. And anything your gaming group lets you get away with. Respectively. At least, these are my answers; your mileage may vary.
To elaborate: The only other difference I'm aware of is also mechanical: Human Guise calls for (the possibility of) discipline rolls when stressed to maintain human appearance, though it provides no guidelines for just how difficult such a roll should be.
An example of a creature with Human Form and not an entire new form, would be, well, ok, nothing in any of the novels I can think of - but consider a minor shapeshifter, one who can, say, add claws and scales, or lengthen limbs for higher speeds, but can't actually totally abandon human form. Or consider someone with a suit of mystical, summonable power armor. No entirely new form, but definitely valid for the Human Form limitation.
