As far as MOBAs go (which are generally known for having steep learning curves), I would certainly consider Heroes of the Storm beginner-friendly. Yes, there are many heroes (but fewer compared to other MOBAs), and there are many maps (though the skeletons of the maps are quite similar due to their "do this objective" formula), but it truly isn't all that overwhelming. On top of this, the talent system is far simpler and easier to get used to than a massive item shop (like we see in League of Legends and SMITE, for example), which is a huge burden off of a newcomer's shoulders.