What Generally Keeps You Invested In Games?

We've all been there.  You'll get a game, and not like several or most things about it, but continue playing it for some reason.  Could range from the act of spending money on it (making you feel like you need to finish it to justify the purchase), to some aspect(s) of the game itself (like only going on because of the story or gameplay, etc.).

In my case, at the very least the gameplay needs to hold up.  If the game plays like shit or is boring to get through, playing it will feel like a chore.  But assuming the gameplay is at least decent, the OST will be the next hurdle.  The OST doesn't need to be catchy, but if it at least gets me invested in what's happening around the characters (atmospheric), then I can trek through and enjoy the tunes.  Assuming both of the former are at least up to par, the story.  This only applies to games that actually have a story of course, so games like PacMan would be excluded.  If there's going to be a story, it may as well be a good one, and one that actually makes me have a reason to care about the characters.  And finally, at the last leg of it all, the graphics, assuming the others are at least okay.  It goes without saying that pretty graphics can mask a terrible game, but if the graphics are at least appealing to look at, and the rest of the game is okay, then getting through it won't be that much of a chore.