Outdated, go here.
Sure, not all RPGs suck. But everyone seems to think that the most important factor for an RPG is it's "plot" or "story". This simply isn't true. Or, rather, it's only true tangentally.
I've recently been on a big thing about how rule sets are the most important thing in a game. So, if you're clever, you might already realize that I'm about to use RPGs as an example.
The most popular RPGs do not have any better stories than generic RPGs which make barely a splash.
For example, Chrono Trigger is undeniably one of the top ten RPGs of all time. Star Ocean II is not. Even though they had the same target audience, the same basic save-the-world plot, the same kinds of characters.
You could argue any number of other factors. Advertising, writing, character design, gameplay... but you'd be arguing wrong. Advertising (or inertia) certainly matters: the Final Fantasy series attests to that. However, I don't think anyone will argue that advertising actually makes a game better. The rest of the arguments? No.
Perhaps you're unconvinced.
Chrono Trigger's gameplay wasn't exactly innovative - it was barely even interesting. Star Ocean II actually had more interesting gameplay. Many non-fantastic RPGs that have no lasting appeal actually have innovative gameplay. 7th Saga, Persona, Parasite Eve, many others. Excellent writing, design, gameplay... these games often have a few people who continue to be fans long after the games are old. You probably are thinking, "Yeah, hey, that was a great game!" But you'd really have to stretch to consider them "top" RPGs, and you probably haven't remembered them in years.
The one thing you probably wouldn't think of comparing is rule sets. By which I mean the overall rule set of the game itself, not just the rules of the game play.
Chrono Trigger has time travel. It has a rule set that uses time travel. In addition to the solid writing and the nearly-two-dimensional characters, CT's time travel schtick allows it to give the player a level of emotional investment in the world and its characters that few other games can match. Also, it gives it some cool plot twists that flow neatly - totally unforced.
Final Fantasy VI (or III, whatever) uses a rule set that allows for many, many different characters. This allows you to build a story that spans dozens of view points and dozens of lives, and also allows you to let the player ignore the characters he doesn't much like.
Most of the really popular RPGs aren't great because of their writing or their plots. Those things are important, but dozens of RPGs that vanish without a ripple have writing just as good and plots just as good.
The really popular RPGs are great because they have a rule set that gives them the ability to produce better metacontent.
The rules drive the content. Generic rules give you generic content. This is why so many RPGs just aren't interesting to anyone other than RPG-heads. They build off solid gameplay rules, but their meta rules are given no thought, and turn out generic and patchwork.
Think meta. :)