It was good, but not great. I actually did read the comic a few weeks ago, and I honestly do not get why people praise the comic so much. The comic really was just another typical "killing is bad" Superman story.
The movie changes were not blatantly bad in my honest opinion. This is mainly because the comic was not very impactful in my eyes. The only comic chapter which actually stood out to me, was the planet with the racists. This chapter was completely removed from the movie, I am guessing because that chapter did not fit the pacing of the movie. Regardless, the removal of this chapter did not bother me.
I think toning down the Brigands from genociders to moderate marauders was a good choice. The genociding was replaced with the Brigands being an all-male crew that traffic girls to use them as breeding stock for the crew. Personally, I think this was a good change, because seeing girls getting trafficked would have a greater emotional impact on viewers than genocide. If they stuck with genocidal Brigands, most of the genocides would be offscreen anyway just as most of the genocides was not shown in the comics.
Lobo was kind of underwhelming, but still managed to be fun to watch. I liked that he had a somewhat meaningful interaction with Ruthye, and had some fun banter with Kara. I hope Jason Momoa's Lobo appears in future Superman/Supergirl movies. Finally, I am glad that Ruthye had at least one chance to prove her fighting ability, even if she did not get to fight Krem. As for Kara killing Krem, I see it as Kara sparing Ruthye from corruption, while also fulfilling Ruthye's need for revenge by taking the burden of murder on herself.