The use of leitmotif
I think that Thundercats has the best musical score of any 80s cartoon, and what really helps to set it apart is Bernie Hoffer's use of leitmotif (i.e. a unique theme for various characters and locations). If I say "Thundertank", chances are the theme pops immediately into your head. Same with "Cat's Lair" or "Snarf".
I really think this helped to create a stronger emotional attachment to this world for the viewer.
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