Finished season 1 and 2. Season 1 was pretty mediocre. The first few episodes were dreadful in terms of pacing. Making the first 3 episodes a 68 minute pilot is a terrible idea for kids animation because it really doesn't hold interest that long. With breaks every 20 minutes it's much easier to watch.
When the plot for season 1 "got going" it improved, but was still kinda meh. I like the idea of them visiting different planets and civilization and having mini-adventures while trying to fight Zarkon, but the season just didn't do enough with the concept. It felt really drawn out, almost like they didn't know if it would get renewed so didn't put in effort until later in production when they knew they could make another season.
Season 2 is way better right from the start. More interesting places, more interesting Robeast fights, more interesting in general. I think the worst episodes in season 2 were the 3 near the end where they split on different missions. The prison rescue was stupid because the guy they were rescuing was annoying as hell. The giant space worm episode was the best of the bunch but still had too much bad humor. The Princess Alura solo was a snoozefest aside from the fight at the end. The best episodes of season 2 were the Space Mall episode and the Blade of Marmora stuff. Keith's melee action is always great to watch.
Best things about the show? Studio Mir's character animation is great. I love the way they animate action, and even their comedic facial animations are great. The most disappointing thing is the quality of the CG action animation with Voltron. Considering it's the part of the show actually produced in the US, I expected way more out of it. Instead it doesn't even look better than the above average TV anime CG that Orange is able to produce, and they're not funded by a big Hollywood studio.
The writing on the show is kinda garbage though. Not digging most of the humor. The only characters I like are Keith and Haggar. Most of the characters are annoying or underused.