I love "trapped in a video game" stories -- be that in books, anime, or even games. As a gamer, such stories directly relate to my greatest passion. But more than that, "trapped in a video game" is setup brimming with the potential for epic plots and thematic explorations.
Much can be done with the "trapped in a video game" setting. It can be used for straight-up adventure or horror. It can bring to life an exploration of the human psyche or be a thought experiment for the construction of a society as a whole.
In other words, it's the way this setting is used that makes all the difference; "trapped in a video game" is the starting point, not the be-all and end-all of the story.
That's one of the reasons I get frustrated when things like Sword Art Online and Log Horizon are called rip-offs of the first popular "trapped in a video game" franchise, .hack//SIGN. It's like saying Star Wars is a rip-off of Star Trek just because Star Trek came first and has a similar setting: a galactic civilisation in space.
Yet despite the shared general setting, we all know these two series couldn't be more different. One is science fiction and concerned with exploration, the future of mankind, and social commentary on our modern day world. The other is science fantasy and gives its all to the creation of an engrossing adventure about heroes and villains battling among the stars.
In the same way, .hack//SIGN, Sword Art Online, and Log Horizon are fundamentally different stories despite having the same starting point -- a "trapped in a video game" setup. .hack//SIGN is a mystery about a single person trapped in a video game and how he (and those players around him) deal with the psychological and game world problems that relate to his situation.
Sword Art Online is an action adventure where thousands of people are trapped in a video game with the ever impending threat of real world death looming over them. It spends its time on action, romance, and an episodic exploration of how various people have adapted differently to the new world. Log Horizon, on the other hand, is not as interested in the individual's reactions as it is in the overall implications of building a new society from the ground up in a game world made real.
For decades, fantasy works have built amazing tales on the backbone of the Lord of the Rings-style setting -- and that's not a bad thing. Video game worlds in any form of storytelling are the perfect setting for future fantasy and sci-fi works -- and the plot device of being trapped in one is just one of countless possible subgenres that can tell any number of enjoyable stories.
So remember: Just because a setting has been used before doesn't mean that other works with the same setup are simply inferior, cheap copies. There are many epic stories out there that start at the same place. And the more creative imagining that can springboard from that "same place" -- whatever it may be -- the better for us as readers, viewers and players.