I watched all three seasons over the past few weeks (maybe the past month? It seems to have gone by quickly, watching a couple episodes a night on Netflix). I thought season 2 was the weakest, and in some ways season 1, I think, is still the best one. I thought the way Alec and Ellie discussed things at the end providing great nuance to the story, which I felt kind of got trampled on in season 2.
I also thought season 3 did a really good job (based on what I know about those kinds of crimes/situations) in handling the topic of sexual assault. I also liked how when the showed the crime playing out, they showed enough to explain and know what happens, without actually showing Trish getting knocked out or assaulted.
I enjoyed seeing David Tennant and Jodie Whittaker in much more serious roles than when they play the Doctor.
And, of course, I echo was everyone else has said in the thread. Ellie and Alec are great characters and I love the way they interact with each other. Ellie is definitely my favourite character in the whole series, too.