Well it’s nice to hear you’ve already past the point where TCW took a decisive leap on quality, so prepare yourself for a treat. Seasons 3 onward feature some of the most nuanced, dark and overall well-written arcs.
We just watched the Darkness on Umbara arc, and it was pretty impressive, especially the first three episodes and most of the fourth. Not a huge fan of the one-note villiany at the end, but other than that it was rather astonishing considering the target demographic.
I concur with you that Krell’s turn could have been developed better, yet I still can’t forget how cold I felt after seeing the clones attack each other.