My favorite game has been and always will be Half-Life 2. The first Half-Life holds a close second, but there is something about 2. The game basically changed my life and is completely untouchable in my mind. The perfect game.
Fallout 4 probably. Used to be GTA SA, now it's either FO4 or GTA V thanks to all the mods! Mass Effect 2/3 were really nice too, but short. And Witcher 3 was nice cause of how big the map is with the expansions, but gameplay got boring quickly sadly. Story's still cool though!