Fallout, of course. Because we need a spiritual successor to New Vegas (and the themes of the first two games).
Star Wars. Ignore what Disney have done, there was plenty of potential there for all kinds of new games - isometric RPGs, KOTOR 3, Bounty Hunter action-adventure games, Jedi Knight 4, TIE Fighter 2, X-Wing Alliance 2... you've got freaking Star Wars as your licence.
Elder Scrolls. Make a true sequel to Morrowind, set in the intrigue of the Imperial City as plots threaten the Empire's collapse.
Mass Effect, because I'm a sucker for space opera. Keep the skills of Mass Effect but with squad-based, turn-based combat.
Jade Empire, because I loved the music and atmosphere of the first game, and playing an evil bastard who can betray and kill your own party members is always fun.
Dragon Age. Deliver a sequel to the first game that improves its systems in every way instead of making them worse.
Alan Wake. Because it deserved an Alan Wake 2 and 3.
Alien Isolation. Because it deserved a second game, introduce some of the action of Aliens, but keep the threat real.
Half-Life 3. Because we've spent long enough waiting for a sequel to Half-Life 2: Episode Two (although it seems things are finally changing at Valve).
Bully 2, because the first one was Rockstar trying something different and it was a lot of fun.
Alpha Protocol 2, not because I think the game needed a sequel, but we need more modern day RPGs. Also, Bloodlines 2. I'm hopeful about it but I fear it will be too cuckish/SJWish/have stupid writing.
Tyranny 2, because that world and those themes deserved a sequel.
Plenty more to add later.