The title of this review sums up roughly 90% of what I have to say about Open Up!; it's a particularly cute and satisfying coda to Birdland. Of course, I could say something about how the characters in Birdland are sufficiently well-executed that it would make me happy that they are happy; but that would really be the domain of a review of Birdland. Play this after playing that one, of course.
In sum: Cute!