I watched the rest of it. The second half improves upon the first by -- at the very least -- piling on setpieces one after another. Supergirl fights some invisible beast at a carnival before recusing Ethan from out-of-control bumper cars. This leads to my favorite moment in the movie with Supergirl carrying Ethan inside a bumper car as she flies some great distance for no particular reason. While she's away, Selena uses her magic to invoke some sort of martial law or something in Midvale, and apparently, only in Midvale. It looks like the lamest OWS rally, as Lucy Lane and Jimmy Olsen wave protest signs and are menaced by shock troopers in black helmets. How I'm describing it actually makes it sound better than what you see in the film.
Supergirl returns to Midvale and is promptly banished by Selena to the Phantom Zone, which appears to be the Swamp of Sadness set from "The Neverending Story." Once there, she's found by Zoltar. He tells her there's no escaping from the Phantom Zone. None. Nada... Oh, wait, but there is ONE way. Supergirl and Zoltar scale a sheer cliff, trying not to fall into a nearby tornado. Zoltar's not so lucky. But Supergirl manages to escape.
Finally, she confronts Selena. Words are exchanged. Floor tiles are rattled. A giant monster tries tearing Supergirl apart, using this weird anamorphic widescreen effect, but is unsuccessful. Supergirl defeats Selena, restores order to Midvale, and then she files back to Argo City with the Omegahedron. The end.
Whew. It's a movie jammed with incident, but lacking any sort of clear, coherent story. It's a movie with a plot like any side-scrolling video game from the 8-bit era.
I read there's a rumored 150-minute cut. Woof.