I wasn't trying to trick my boss. I really do spend almost all of my time on the internet looking at video game websites such as gamespot, IGN, gamefront, super cheat, exc. I know more about video games than anybody else in that store.
Tough lesson to learn, dude. Sorry it cost you a job to learn it. I don't doubt you do know more, but that's probably not a primary job factor.
Unfortunately for you, your boss is probably more interested in you interacting with clients and selling games than he is interested in you knowing a lot about them. The average customer in the store isn't probably THAT impressed with your knowledge; he is looking for a good, quick deal, and can do his own research online. In fact, I would bet the boss doesn't want you to get into long detailed conversations about games, using your knowledge to teach the customers. That slows down his cash register line, and quite possibly costs him customers who get educated enough to go elsewhere for better deals (face it, Game Stop isn't the cheapest deal in town by a long shot).
This focus on clients over smarts is probably true of most businesses, too. For example, most employees at Best Buy don't really know all that much about the tech that they sell. If you're even reasonably tech-savvy, you can smell the BS 10 feet away. I wave off the help almost all the time, because I can tell they don't really know anything serious about the gear, even if I don't either.
Your word "almost" (as in almost all of your time) is worrisome. Boss is probably unhappy with the other fraction of your time. I suspect you've been warned about the issue, and it was more your refusal to follow the rules established for you, than anything else. Boss simply wants someone to always do what he says, because he can trust them more. Given a choice between an untrustworthy, rebellious guy with serious game smarts, and an average guy who simply follows instruction, he'll pick the other guy every time.
So if you want a job to fit your parameters, you'll have to either find one or create one. It's unlikely you can redefine a job to fit your interests.