I didn't need her fleshed out more, since I felt she served her purpose. I think the only thing missing for me was if they established whether or not they were always experiencing their dreams. Of course, we have the answer, but I think that was the missing piece. That, and the timelapse.
Perhaps, but she was the main villain and she had no story. She was essentially a henchmen in the role of the main antagonist. I would've been ok with the presented version of events if they showed someone else from Essex Corp in the shadows. And it didn't necessarily have to be Nathaniel. They could've explained how her forcefield still worked even when she was asleep or even knocked out. Why being a mutant herself, she chose to do this testing. I mean, she seemed opposed to it...but carried out the orders robotically. That's henchmen status.
I felt like Illiana should've talked about her brother at least once. Explained who the Slenderman was that terrorized her.
More backstory would've helped explain the hallucinations. Sunspot killed his girl...at least show some scenes in the past showing his relationship with said girl. Same with Wolfsbane.
Another 30 minutes and this could've been a B movie.
This felt like The Faculty meets Freaks but none of the charm because they didn't even bother to write the charm.