Season 1-3:
It is a solid series with decent action and suspense. The unfolding of the story is nicely paced and has you really on edge between each episode.
Personal development as a character is not really noticeable in my opinion. But not regarding that, they characters still great and likeable. And they don't do anything that wouldn't seem in character.
Season 4: Had a very good build up, but the last 2 episodes really rushed it. Like, it undid the whole story in my opinion. I feel if they made 2 episodes more, they could have closed the series more successfully. Everything went so fast, and some things happened out of extreme luck that I was thinking. This is not right, this should not have been that easy.
TLDR: 1 - 3 season very nice, 4th season meh.
Personal development as a character is not really noticeable in my opinion. But not regarding that, they characters still great and likeable. And they don't do anything that wouldn't seem in character.
Season 4: Had a very good build up, but the last 2 episodes really rushed it. Like, it undid the whole story in my opinion. I feel if they made 2 episodes more, they could have closed the series more successfully. Everything went so fast, and some things happened out of extreme luck that I was thinking. This is not right, this should not have been that easy.
TLDR: 1 - 3 season very nice, 4th season meh.