There are some interesting ideas in here and it has the makings of potentially a good love story. But the writer really needs to focus on John's character arc and develop Carol's illness a bit more. The ending falls completely flat because of those two aspects. The writer also needs to give John and Carol more to do together. A couple casual dates does not equal a strong relationship. The marriage proposal comes quick and out of nowhere because it doesn't feel earned.
Writer needs to work on fleshing out the concept for this. It's unclear what the addiction is really supposed to be, and the health risks need to be defined more clearly. Carl needs to be given more emotional depth and more of a backstory. He also needs to show more character growth.
Overall, there is a market for this type of film. The horror community loves this type of stuff. And home invasion thrillers are pretty easy and cheap to make. However, the writer needs to focus on giving this story more of a purpose for existing. Currently, the story is very weak. The break-in happens, violence ensues and most of them die. It's a pointless exercise in violence and the story completely falls flat. Giving the characters more compelling goals would breathe more life into this and perhaps help the story find its purpose. The antagonists need to be smarter, and therefore they will have a much more formidable presence and seem like a bigger threat. And if they have a better reason for executing their break-in plan (not just going after a trophy), it would be more compelling and probably scarier. Fleshing out the characters, giving them each more personality, and making the protagonists more relatable would make the audience want to root for them. In the current draft, the audience won't care of they live or die.
A cynical college student suspects something is amiss when her eccentric lab partner reveals she has a son.