When I was a kid, I was enthralled by the lore of Sonic games. Mainly the echidna race, the chaos emeralds, and eventually the character Chaos. Then Sonic Adventure 2 came along and I lost interest.
Anyway, since then I was never particularly arsed about it (disclaimer: the Arkham series doesn't really count considering it's an amalgamation of the comics and DCAU) Even in Shenmue and my favourite series Splinter Cell. I wouldn't even care about the story or impending threats in the latter at all. I very much had the attitude of "shut up, just tell me what to do and I'll do it without anyone ever knowing I was there."
Then Skyrim came along and changed everything.
I'd previously played Oblivion and was bored shitless by everything, though extremely addictive. In Skyrim though, I cared about everything. I was constantly torn between who I should back in the civil war. I wanted to learn as much as I could about the Dwemer. I genuinely despised the Thalmor. I even found myself conflicted as to whether or not I should do the Malacath quest. Up to that point I'd been very anti-Daedra, but after learning more about him, I almost felt obligated to help out the Orc tribe.
I've never been one for D&D or fantasy type shit, but The Elder Scrolls has become an exception (except Fable, but I see that more as a comedy) I have to take my hat off to Bethesda for making me sink hours into reading more about the lore, watching the Shoddycast series, and compiling an ever-growing list of mods to install for my eventual second playthrough.
So, what games grabbed you in a similar way? Which worlds did you go out of your way to learn more about? How much longer did you spend researching fictional history than you did our own?