There isn't a show on TV that can sustain a massive launch like Supergirl's premiere. With a staggering 16 million viewers in the Live+3 (12.9 million in live alone), of course it was going to have a fall in week two.
And fall it did, to a Live rating of 2.2 with 8.9 million viewers. That's a drop of about 29% week-to-week, the largest drop of a new series this fall. Time-shifted viewing will be interesting, especially since the CBS series goes directly head-to-head with fellow WBTV and DC Comics adaptation Gotham over on Fox.
As for Gotham, it saw a slight rise, with a tenth increase in ratings to a solid 1.6 with 4.3 million viewers overall. With a planned story split after the eleventh episode, Fox still hasn't announced whether that also means an early hiatus. If it does, we could only have four new episodes left in 2015, with the other 11 airing in early 2016. They started November sweeps a bit early in Gotham City with death, dismemberment, and the rise of another villain.
Monday Night Football, as usual, won the night overall. Supergirl tied with Greg Berlanti's (that guy is everywhere) Blindspot as the top scripted show of the night - so it's not all bad news for the Girl of Steel.