VOY had quite a few plot threads that developed over time - especially the characters grew and developed more than on any other Trek series except DS9. Prime example being the Tom Paris - B'Elanna Torres relationship and Seven of Nine's growth as a character and becoming part of the crew. Other, smaller relationships also developed over time, Tom's relationship with his father, the Janeway-Chakotay early romance/relationship, Janeway becoming a more hardened leader and later a more motherly mentor to Seven again, the Doctor starting out as the character that had to
learn how humans work vs. him later
teaching that same thing to Seven, Harry's growth from a greenhorn to a professional (although never raising in rank...), Chakotay reconciling with his spiritual side, Naom's growth, and many, many more.
There were some major plot changes to the status quo as well: The Doctor gaining his personal emmiter, the first contact with Earth was a major milestone as well, species and regions were left behind as the Voyager moved on during it's journey, and lots and lots of plot threads (Borg/8472, the Hirogen and holotechnology) all were visited and revisited multiple times and had a very clear story progress.
But all that being said:
Every single episode was stand-alone.
After the episode was over (weather it was a two-parter or a single episode), that plot was resolved. If it was revisited, they had
a completely new story that continued that plot. NOT a single, serialized story arc. The actual
progression of characters and plots happened always in the
background of the episdes, it was never the A-plot so to speak.
So yeah,
@DigificWriter is right in that there were many serialized
elements in that show. But the show
itself as a whole surely wasn't.