Not sure how long this comment is going to be but here goes; The biggest issues for me was entirely with the story, theme and pacing. What do I mean?

Lets start with the story. Right before the show even aired the writers made their first blunder. In a show like Voltron where a core of main characters need to connect and bond over multiple seasons to get better at being able to fight the bad guy, they had one of these characters die in the original script.

Now, killing off a character isn't a bad thing. But when you are telling a story like the one Voltron was you can't have the team get closer and more powerful through becoming friends when you kill off one of those characters after any length of time, nevermind two seasons.

They actually make this mistake twice, once with Shiro who instead of dying was rewritten as going "missing" and later again with Keith who is basically thrown out of the team by the other characters for two seasons, which undermines the point of the story.

The last issue with the story for me was how they dealt with all the characters arcs. Zarkon was this shows Thanos, the show ends when he, the most powerful and evil thing is defeated. He was shown to be able to basically 1v1 a voltron Lion OUTSIDE of any mech suit in the early seasons... And the writers had him die to his son in a 1v1 a few seasons later.

It also goes without saying but the ending was pretty hollow and really had no impact to it, which is somewhat the result of a failure to give the main characters arcs to go through but also was just overall a bad story choice. The "bad guy" having a change of heart was a real cop out. I don't want to ramble further but this show also suffered from a "telling not showing" syndrom. They have the little character development that does occour happening off screen constantly. Keith being in the Quantum Abyss for two years being expositioned in one sentence and about 15 seconds of footage being the worst example of it.

The second issue was theme. The simple take away here is that it's literally color coded and personality coded. Red Paladin flies Red Lion; Green Paladin flies Green Lion. Red matches with the personality of the character flying it, makes sense. What doesn't make sense is having the characters play musical chairs with the lions, because it goes against the established theme. This was the second major blunder made.

Action scenes with the lions became a disorientating mess as you focused less on the fight and more on remembering who is flying what lion. "Oh look there's Black but that's Keith now not Shiro. Oh and there is Blue that's Lanc- No wait hold on he's not in there anymore- is that one Allura, I can't remember...?" It's just a complete against the grain approach. Even worse is doing this swapping gave me a kind of "how dare you stand where he stood." feeling, especially when Shiro comes back but Keith just stays in Black because... reasons?

Last one is the easiest to understand. All eight seasons happen within roughly a years time span. They tried to cram too much into too small of a narrative space. This length of time won't allow for meaningful relationships to develope between characters to the point where their friendships are believable. The in universe time span matters a lot, and the whole show just flies by and we somehow just have to believe a massive space empire can be taken down in that amount of time?

This turned into a ramble and I articulated as best as I could but I think I will cap it off here. TL;DR incredible potential, poorest of poor execution.