I watched the first season on Netflix and thought it was fun. The second as well, but I'm not far in. I much prefer the Flash. But I'm not a huge DC guy so don't feel the connection to the characters or world prior to adaptation.
LEGENDS can be a bit inconsistent, but I thought SEASON 2 was a lot more fun than the downer storylines in ARROW and FLASH. I think the show works best when it doesn't take itself seriously like with the George Lucas and JRR Tolkien episodes.
LUCIFER sucks as an adaptation, but as a generic cop procedural featuring The Devil, it's grown on me.