Looks really promising! I would rate the game, but I believe it's better that I just leave a comment with my feedback and rate it once it's complete and not a demo.
THE DOOR has a nice visual style, simple controls and a really charismatic character that accompanies you along the way. There are a couple of issues that are normal in a work in progress. For example, objects clipping each other when completing a puzzle, which kind of breaks the visual effect. Also, pressing Escape makes a menu appear on top of the game, but doesn't actually pause it, which feels weird. Apart from that, I'd say the puzzles are a bit too easy and Cell-44 offers hints way too frequently. Personally, I like to be a bit more challenged by puzzle games, otherwise I get bored soon.
I didn't get bored with this demo because, well, it's too short for that, but the story also has a certain mystery that keeps you hooked, and I like Cell-44 so much! She's nice and funny, and I want to help her, but part of me feels in danger and even fears she will betray me, at the same time. I must admit I had completely forgotten it was just a demo when I finished playing and the story was left unfinished. Now I want more!
Something more before I post this (and if you're reading this, maybe consider it an spoiler, even though it's been mentioned in other comments already). Word of advice, though this might be my personal opinion and other players might not share it: it's really creepy to see my webcam light up when it's not supposed to. It kind of felt like an invasion of my privacy to have my camera take pictures of me without explicitly warning me beforehand. Now I know how it was used in game, and I think it's a really clever use of it because it contributes to the underlying creepiness of the plot (and warning the player beforehand might spoil the experience), but part of me feels a bit uneasy at the same time. Apart of that, as other players have said before, not all devices will have a webcam available, so relying on it could become a problem.
Sorry for such a long comment... Anyway! Might need a bit of polish here and there, but THE DOOR looks really promising! Great job, keep going! :)