There's a point requirement, but it's pretty lenient. At the end of the sixth stage, you need to have over 2.5 million points. If you have less than that, you get the bad ending.
Little known fact, but there are also different congratulations screens depending on your score. If it's less than 3 million, you just see your team on the screen. If it's between 3 and 4 million, you get your characters plus some others. If it's over 4 million, you get all characters plus fireworks. (At least, I think that's how it goes.)