Well you didn't specify if it had to be a PC game, so;
Metroid Prime Trilogy - Full of lore, an amazing story/plot and even though some people knock the Wii for its less than lackluster hardware it displays some extremely impressive visuals. You explore one area, leave it mostly unexplored and then come back to the same area multiple times to make sure it is fully explored, every secret and puzzle discovered and solved. From Prime, to Echoes, and finally to Corruption, this game has been my absolute favorite since it's release back in 2009 and nothing else even comes close. Picked it up for a tenner in GAME, funny how it now sells for £150 on amazon.
I do have a (rather active) steam account if that's coming into question.