It's been adding a new quest every day, I think (and hope) it at least lasts another week or so.
And yeah, there's more to it than pets as rewards. In fact, the quest to get that particular pet can be quite long and tedious if you don't know where to look. But the black-green crystals (BOE) and companion customization sets (BOL) may be worth it, depending on your taste. Or the extra codex entries, if that's your thing. You do need the defeat the special world bosses to get the last three, I think.