These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Ear Worm: Simply say "AH AH AH AH, AH AH AH AH" to anyone who's watched the series and see them start ramming their heads against the wall.
This Troper personally knows someone who ended up mimicking Nono's walk in the OP while listening to Groovin' Magic on his portable music player.
And then subverted straight to hell and back, as Nono does not remotely need anyone to protect her.
Most Wonderful Sound — The Buster Machine March, reused from GunBuster. Subverted in episode 4 when the Variable Gravity Well is revealed. Then played epically straight.
The opening song. Yes, the entire thing.
Tear Jerker — Many moments stick out as tear jerkers: but the ending sticks out as the biggest instance of this in this series for this troper: "That night, Buster Machines No. 1 & 2, and their pilots, returned to earth. Welcome Home."
Nono performing a Heroic Sacrifice, and leaving Lal'C with a piece of her singularity in the form of an origami crane. A poorly done one, at that.