These are my impression between the difference. Do note it's been so long since I watched season 1 so I may not be super accurate. I remember that in
- In S1, colors are more vivid. Season 2 seems to lean on darker colors. Although thise dancing ladies are so prettyy!
- More fight scenes in season 2. Thank God it's not heavily reliant on CGI
- Season 1 has memorable OST (I love it so much). Season 2 OST is bland.
- Season 1 has a lot of mystery. I think on the first few parts a mystery spans 1-3episodes unlike in season 2, a mystery is almost 6(?) episode long.
- Romance felt forced. In season 2, the romance started to get better especially for PXJ and LLF because in S1, LLF is so in denial of his feelings. But really, they can definitely work out as best friends, I don't see the need forr romance.
- PXJ talent is given more highlight in season 2. In season 1, I felt that she was like a filler character.
- Their bond in season 2 is so stronger. Every character has their own strength and seeing them working together is just so satisfying.

All in all it was still good!
Btw, I just want to say that the wife of both Dugu, portrayed by Xi Wang, is so pretty. Actually, all female side characters are pretty.

Regarding the cases, my favorite are the last two.