For me, Season 1 was mediocre but with some solid episodes plus I liked the cast a lot.
Season 2 I really liked! I loved the Kara/Mon-El romance.. I also thought Tyler Superman was pretty decent in the first episodes, but then the writers pretty much ruined his character in the season 2 finale when he declared Kara was a superior hero than him.. That was character assassination to me.
But I still gave Season 3 a chance for the cast and to see Mon-El back and the Legion... Well all of them were a big disappointment for me and I never cared about the World Killers story. Even when Kara's mom turned out alive, the writers managed to pretty much disappoint me. What a waste of casting with Erika Durance.