Martha doesn't bother me. I understand why it could stop Bruce cold. Its so random, and the very last thing Bruce would expect an alien godlike being to utter when he's about to be killed. As far as Bruce knows or cares this thing isn't a man. He's a monster in sheeps clothing. A demon. And the last thing it seems to care about before it dies is Martha? Then you factor in that its Bruce's mother's name and its no wonder it put him off. Bruce has a serious complex about his parents. Particularly his mother.
So yeah when the demon alien uses what may be its last breaths to say the name of your dead mother and asks you to save her its pretty damn shocking.
The only problem I had with the scene is Henry's delivery and the way its choreographed. The way Henry forces out, "Save Martha." like he's trying to drop a log in the toilet combined with the look on his face is just awkward, and a tiny bit goofy.
Superman should have begun to say, "Save my mother Martha." Bruce should have stomped his boot down into Superman's throat violently when Superman got to the word mother cutting it off, then Bruce should have lifted his boot, and thats when Supes should have rasped Martha weakly when Bruce was bringing the spear down on Supes's throat. Bruce should have stopped the spear just before it plunged into his throat and should have growled, "What did you say?" touching the spear to Supes's throat burning him. Superman croaks out Martha one more time, and Bruce gets angry and is off balance by this point, and screams the question again. That's when Lois comes running in.