This is just a general review of what I felt overall having just finished the finale.
The first season was brilliant, 8/10. If you haven't watched JJ then just watch S1.
The second season was rubbish and so was the third, 5-6/10. Hence I downgraded my overall rating from 8/10 to 7/10.
Trish Walker was such a lame character and the fact that she features more prominently in the plot for S2 and S3 probably explains part of why the show went downhill.
S3 was the end for the show just in the same way as Daredevil which itself was a brilliant show and didn't really dip the way JJ did (blame Netflix/Disney).
JJ for the average viewer can feel like a bit of a drag so bare that in mind, but again it's worth it in S1 as the whole premise is she's a private investigator dealing with a bad guy/girl over the series.