New Vegas was my introduction to the Fallout series.

Is it worth going back and playing Fallout 3 or should I wait for Fallout 4?

Fallout 3 is worth playing.

It is a good game.

We do not know when FO4 will be coming out.

You might find some of your favourite New Vegas features missing, but it's a great game and you'll feel right at home.
Be sure to get GoTY for all the DLC, so you can continue playing after the credits roll and all the extra content.

Definitely worth it, it's got more of an immediate post apocalyptic wasteland feel than New Vegas, and is more focused on the exploration side, but it's certainly worth a try. There's less emphasis on survival, so no hardcoe mode, and no skill magazines, crafting ammo, campfires, or iron sights so a few changes. Some prefer New Vegas, some prefer Fallout 3, but both are very good games.

I enjoyed them both for differnt reasons.

FO3 is a raw action RPG and one of my favorites of all time. Lots of adventure and craziness in some of the stories.

NV is a more grown up adventure with a better overall story and better game play. I didn't relate to the NPC's as much but it is still amazing.

For my money I had more fun and would still go back and play FO3 today.