Silent Hill has quite great storyline all in all but it's relatively simple and not incredibly deep. Halo has quite a rich lore as does Gears and Resident Evil (yes, really) but you've really got to go through the novels (graphic or otherwise) to get it. The amount of Lore in WoW is about on par with the amount of hentai there is of it (lots.). Tomb Raider has lots of Lore, although it's mostly all horse shit in my opinion.
I'm gonna say the series with the richest lore is probably Warhammer 40K, for obvious reasons...
I'm gonna say the series with the richest lore is probably Warhammer 40K, for obvious reasons...