The Four Swords games weren't made to compete with the single player games, but to add some variety to the franchise.
In my opinion, the Four Swords franchise has some incredible potential, but the two true
FS games that have been released so far have failed to meet that potential. The original
FS was too simplistic in its level progression, but the puzzles were excellent because they forced simultaneous play.
FSA had much better level progression, but the puzzles were too simplistic because one player needed to be able to cope with the controls.
With online play, the developers have the means of properly realising the potential of multiplayer Zelda, and I will be excited to play more
FS games in the future.