I am likely to play through a game more than once if at least one of the following applies:
1) The game has a great story that is well-written and has some twists and turns along the way. Bonus points for stories that really make me experience different emotions and/or want to keep playing just to find out what events unfold.
2) The game has believable characters that have their own personalities and flaws, just like real people do. Bonus points if I can really relate to a character.
3) The gameplay offers multiple options and approaches, e.g. via different specialisations or character builds. Even if I never explore all such options due to one of them being a favourite (*cough* Skyrim stealth archery *cough*), having the options is always nice. You know, in case I one day decide that I want to try something completely new.
4) The game has an open world with plenty of stuff, ranging from quests and collectables to random chests and items, to find.
5) The game offers fun things to do when I do not feel like doing quests, collecting crafting materials, or anything like that. Examples include but are by no means limited to following NPCs around, using game physics for various purposes (e.g. stacking items or dead bodies), using spells for more unusual purposes (e.g. using Skyrim's Telekinesis to launch dragon bones at NPCs), and simply idling somewhere admiring the game world.
Things like good combat systems (e.g. Witcher 3) or fun minigames (e.g. dice poker) on their own will not make me re-play a game, but they do affect how likely I am to do so.
Of course, the game also has to be one I like the first time around.