I have no idea, but at 8.75, it's worth it to get both games, plus the expansion. Overlord + expansion, works out so that you're paying 1.25 for overlord 2. It's a no brainer even if it only lasts for an hour that's a good deal.
If you just want overlord 2, buy the package deal because it's CHEAPER than buying overlord 2 on it's own. If you buy overlord 2 on it's own, I will write about it in my signature.