Everyone knows that any given statement can be objective or subjective, where objective means that there is a precise and uniformly agreed upon criteria for determining whether it's true or false, and subjective means that whether it's true or false is entirely up to the person you're asking. What people forget about most of the time, however, is that there's a 3rd category these statements might fall into called "normative." Normative statements are ones that are clearly not entirely up to the person you ask, but ones for which it's difficult to determine how you might decide it's true or false. For these statements, we defer to a normative standard of evaluation and compare the statement to it. Confusing? Examples will help:
The statement "Brendan Fraser is in the movie 'Journey to the Center of the Earth in 3D.'" is objective. We know exactly what we need to do to figure out if that's true - we generally understand what it means for a person to be "in" a movie, and we could determine if Brendan Fraser qualifies by simply watching it.
The statement "I hate 'Journey to the Center of the Earth in 3D.'" is a subjective statement. Whether it's true depends entirely on whether the person who says it thinks it is.
The statement "'Journey to the Center of the Earth in 3D' is a better film than 'Star Wars: A New Hope.'" is a normative statement. If you heard me say this (assuming you've seen the god-awful Journey movie and Star Wars), you would not only disagree with them, but you would say I am wrong. There's a reason for that. This is because there's a generally agreed upon (though admittedly vague and nebulous) standard to which most people appeal to when assessing the worth of a film. You talk about special effects and acting and cinematography and things like that, and within those there are even deeper normative questions about what qualifies as good acting or whatever.
I know what you're thinking - these "normative standards" are ultimately made up by people, and since they change with the whim of those same people, they too are subjective. Well, maybe so, maybe not - it's complicated. But if nothing else could convince you that there is and should be a distinct class of statement different from both the subjective and the objective, it's this: essays. If you've ever been in school, you've probably written an essay or two. When your teacher gives you a grade on it, they're making a statement about how well you did on that assignment. Would you say that statement is objective or subjective? If it's objective, then why do different teachers grade the same papers differently, even though both evaluations might be fair? That would be like two different people solving the same math problem for different answers, and trying to say that both are right. But if it's subjective, then what right would you have to object if that teacher gave you all F's? If that happened, you would be right to argue that what you wrote was worth more than that - and you would likely refer to a normative standard of evaluation to justify your argument. Luckily, many teachers provide just such a standard - a rubric.
The point of all that bull shit was to say that when people argue about "opinion based" topics, they may actually be arguing about normative statements. So when someone says "this game is bad because 'blank,'" they could be right to say that, and his opponent's reply could be valid. Conversation doesn't need to just stop whenever it's not clear how to figure out the right answer. It's a mistake to call all things that aren't simply true or false "subjective" and let every such statement stand as reasonable as the rest. So the next time someone tells you the Jonas Brother's are our generation's Beatles, you can feel justified telling them they're fucking thick.