10 Video Game Sequels That Resolved NOTHING
6. Splinter Cell: Blacklist
2010's Splinter Cell: Conviction revealed that there was a shadowy, globe-spanning organisation called Megiddo that was attempting to covertly control the world, having even infiltrated the Third Echelon spy outfit itself.
Though the game only vaguely hinted at the full extent of Megiddo's influence, it was clearly a thread that was to have enormous implications for future games...only for the for the next sequel, 2013's Blacklist, to inexplicably ignore it completely, save for a brief mention in the game's SMI database.
As such, we're left to assume that Megiddo is still out there somewhere pulling the strings, given that this significant plotline has never been resolved, and it's unlikely that any potential future games will ever pick it back up again.