Great final season, started off slow but really built well through the middle... different from the first two seasons which started off quickly and then got a bit stale through the middle.
JJ, Trish and Malcolms story arcs throughout the 3 seasons were pretty damn good IMO, especially Trish. I can get why some people don't like Trish she is extremely intense which can be offputting but I thought she had a very compelling story. Towards the end of season 3 she showed the same kind of unwavering belief and determination that she was exhibiting when dealing with addiction in season 2.
Ritter embodied JJ wonderfully, the casting was really spot on. Villain in S3 was strong and showed menace without even being powered - similar kind of issue superman often has to deal with. Enemies that he can easily beat, but he's constrained by rules/morality. Unpowered people can be a threat because they're willing to do anything.