While not as mind-bindingly complex as other games on this list, Mass Effect earns its place through the sheer detail and depth of its universe and lore recorded within the game's glossary, known as the Codex, which meant that players had to submerge themselves within a enormous wealth of information in order to fully comprehend the plot. A space-faring adventure also meant players had plenty of history to learn as well as the number of new alien species to memorise as protagonist Commander Shepard navigates the Milky Way over the course of the trilogy. And of course, the now infamous ending to Mass Effect 3 threw another spanner into the works as fans were outraged at the seemingly pointless ending to Shepard's adventure, so much so that petitions sprang up almost immediately, appealing BioWare to change it. A entire trilogy was very nearly ruined by some clumsy writing on the creators' part, only to be averted at the very last minute with the release of a new extended cut of the ending.
