I own Worms 4 and Worms World Party, so I will base my idea of 2D Worms on that.
Worms World Party has more stuff (weapons, maps etc), but Worms 4 is a better game due to its being 3D. At first I mourned the loss of some weapons, a lack of maps and having to get crates more, but once I got into it, it was a much more fun game.
Because the game is 3D, it has better graphics. The extra dimension also adds some fun challenge to the game over 2D versions. E.g, in 2D versions, knocking an enemy worm into the water could be as easy as facing left, choosing baseball bat weapons and firing. Now you can't just point left; you have to aim properly.
Although it has less stuff than World Party, it has better features. You can design your own weapons, and save your game styles, which I couldn't do in World Party!
Conclusion: Less ‘stuff’, but more features, better graphics, and more fun gameplay.