Yeah, without a license, you can use the basic rules, and a limited selection of spells and such, but you can't have anything to do with any of their lore and campaign settings.

I don't think they have a limited license as such. The open license is a bit murky about your obligations, particularly with regard to use in a computer game. I think they just got WotC's blessing to use the open system, to avoid any potential legal hassle.