Its a good solid demo. The upgrades are worthwhile. It can get really tense dealing with enemies whilst trying to keep the fire burning.
I didn't quite get that torches help you survive outside the fire at first so I died a few times to that. I had a bit of difficulty judging exactly how close I needed to be to pick up items. I kinda cheesed it once I realised that enemies don't spawn over 30 fire, so I kept the fire around 15-25 and had a relaxing time.
Good job!