Reasons why I think he had a soul all along (and didn't gain one later)
Look! A thread actually dealing with content of the film instead of a "Dis Sux!" thread!
My reasons why I think Adam had a soul all along:
Keep in mind, I have not seen it yet. I just know spoilers. I have read the prequel graphic novel and the actual Mary Shelley novel.
1. In Mary Shelley's novel The Frankenstein Monster fully believed he had a soul. He talks about it many times and at one point questions if he's a new soul or the soul of one of the dead men and aniamls he's made from.
2. In most religions the soul is your consciousness able to live on after death. "It's not that I have a soul. I am a soul. I have a body." - Harry Dresden in The Dresden Files. But then again this film's theology is strange.
3. The free prequel graphic novel I, Frankenstein Genesis tells us that The Gargoyles can be wrong about people not having souls. In the backstory about Leonore the demons plan on tricking the gargoyles into accidentally killing humans (which they are forbidden from doing and results in the Gargoyle's own death) by hiding among humans in battle. The other gargoyles were unable to see the light in these humans until Leonore warned them about what the demons were planning. One even says something to the effect of "Why wasn't I able to see the light in them before?"
4. The Gargoyles went out of their way, convolutedly, to convince The Creature that he has no soul in the graphic novel prequel, going as far as to have one of them pose as a woman for a year to trick him into thinking he's in love with her, just to tell him that he's soulless for wanting to stay with her. (Because it would put her in danger, apparently...) Why do that if he does not have a soul? This hints to me they (or one or a few of them) know he has a soul but have a bias against him because of how he was created.
5. We are told in the graphic novel prequel that gargoyles cannot kill someone who has a soul (a human), that gargoyle would die instead. Repeatedly in the graphic novel prequel graphic novel a gargoyle would either be talked out of killing Adam or would make up an excuse to not kill him. This suggests to me that they, at the very least, suspected that he had a soul.
6. They say only someone soulless can kill a gargoyle but at the same time a Gargoyle cannot kill someone who has a soul. That gargoyle will die. They never say how. What if Gideon's death in this film was the fulfillment of this notion, that if a gargoyle tries to take the life of someone with a soul he'll die instead. They weren't exactly specific how the gargoyle would die.
7. It was the acknowledgement of his identity (and maybe realizing he had a soul) that made Adam able to resist the demon at the end.