Hey Gorka!
Big fan of your videos, they really helped me when I was first starting out. I gotta give you props on the character controller as just moving around in the space felt really good.
My biggest criticism is this feels more like a tech demo/mechanic demo than a game. I think adding a system to score you based on how much of the building you painted in the time frame. Then maybe a system where your brush runs out of paint so you have to run over to where the buckets are to refill your brush.