Not including Black Lightning which had a very good short season one, Supergirl and Legends were the most consistent shows last year. Supergirl is going to be very different this season with the main cast changes and others involved in different storylines not interacting as much with the main storyline (Martain Manhunter).
I feel it's a make or break year for the CW DC shows. Arrow is sort of running out of steam, and The Flash was OK but the last two seasons haven't been that special.
Another challenge for Supergirl is the new timeslot of Sundays going against the NFL. That's going to be tough.