So, is he supposed to be good, evil or some kind of neutral?
The anime just says he's misunderstood, so do some of the spinoffs. But then in the mainline games and Mystery Dungeon, he's just completely evil.
Not to mention his very presence causes sleeping Pokémon to suffer.

It just seems to be that Darkrai's genuinely evil, but every spinoff aimed at an even younger audience and the anime shows him as good...