Every RPG needs certain things. And RPG needs to have many things, and these things, even though some are small and you won't notice them, will make the game feel broken if you don't have them.

1. EXPLORING

Exploring the land comprises the meat of most RPGs. Exploring should be enjoyable, not a chore. There needs to be things the player can discover by themselves by experimenting, and when they do, they need to be rewarded by it. A big game world offers much oppurtunity to explore. An extra thing that may be good is making sure there is always some subtle way for them to find there way back. An example is in Dragon Quest VIII. The fact that you can see landmarks from a great distance means that you can never get lost.

2. CHARACTERS

You're characters should be good, regardless of what type of game you're trying to make. Earthbound had it's NPCs able to hold meaningful and hilarious conversations. A good NPC is one that says things that are entertaining, changes his dialogue regularly, and isn't there just so you can practice you're smiting on them.

Alternatively, you can make every character funny and nothing extremely serious, and remove all traces of Angst. An example of this is Paper Mario, and it works beatifully.

3. STORY

A good story is one that isn't extremely generic. If it is, make the locations and characters interesting enough that the player won't care, or won't notice. A good story doesn't nessecarely have to be an earth-shattering huge thing here. It can just be a simple quest to restore the humanity of the king. A truly original story is one without angst, lots of humour and very quirky.

The initial concept of the story doesn't have to be mindblowing, but it's help if the game actually made it a good story as you went along. An example is Okami: This game's story is generic, but the way it's implented isn't. It has plenty of humour and warmth, which makes you empathize in ways you wouldn't have with the character's without it.

4. COMBAT

Face it. Everyone loves a good beat-up. A good combat system is important, so you have two paths you can walk down. There's either Turn-based or Real-Time.
Both have their advantages and disadvantages, but there numerous and i don't have the time to list them all here. Because there are many. Examples of good combat systems are Paper Mario, and the simplicity of The Legend Of Zelda: A Link to the Past. Notice how i didn't say Final Fantasy? Because of Random Encounters. The're utter feaces.

5. ENEMY DESIGN

You're enemies should be original to all the other enemies. It should have at least three attacks, and a few little twists. Like the Zora in The Legend Of Zelda. The trick with them is they constantly warp, are in the water and a pain in the gluteus. As are the Lileeps.

NOW THE HARD PART

Tying all of these elements into your game can be hard, but it will pay off. It's possible to do, and i've seen it done right in three games:Paper Mario, The Legend of Zelda, and Jade Empire.

Now you're finally ready to make you're RPG!