Metroid Prime: Echoes is, in my opinion, a step backwards from the original Metroid Prime. A lackluster story, uninspired weapons and a poor multiplayer mode all come together to create a disapointing experience to a very highly anticipated game. The addition of the Dark World is merely the developers way of getting out of having to create an additional area to explore.
On a lighter note, the graphics are quite impressive but not noticeably different from the originals.
Overall, Metroid Prime 2 is not nearly as good as the first and is better off avoided.