I think that while it may have seemed melancholic, it’s certainly sad with how it ends from Yondu’s perspective, but I think that the principal arc of the movie as a whole is the idea that the Guardians are a family, and they’re a family that’s trying to lear how to stay together and to be a family.
So from that point of view, I think there’s an uplifting element of it, even though it’s sad because of the death.
And from that perspective, it’s actually a very happy ending because they are all together at the end of the movie.
I think that even though he finds the friends in the first movie, it’s pretty clear that Rocket still feels alone for most of the second movie, and that’s why end on his face, is that I think that he’s learned to be more of a family member to everyone.