Wow! Not only is The Subspace Emissary quite big for an add-on, but the storyline is vastly surprising.

In my opinion, people took it for granted because of certian rumors and such. However, you will find many to be false. In fact, playing The Subspace Emissary the whole way through is the secret way to easily getting most of the charcters. You will be able to get all but a few charcters this way. In fact, most of the charcters you won't have to battle to actually get them if you do this little thing. It is highly recommended for those who aren't too good at the brawls.
Now, the storyline is quite amazing. One minute you believe something about it all and then it just shatters it with some of the most surprising twists ever. In fact, near the end, it is quite shocking. Oh, and if you beat it, you get a full translated version of the opening song to boot. However, let's just say they were better off keeping it untranslated. At least, that is my opinion.
Regardless of everything, I suggest everyone to play it. It'll be well worth the 5 hours you'll more than likely spend trying to beat it. (Yes, it only took me that long.) With all the stuff it unlocks in the end, it's more than worth it to play.

Now, if you'll excuse me, I need to try to find a new time to play on-line. I'll see ya later! :^.^: