In fact it is already the case, Marcin. If you look carefully you will see that different areas are separated by full lines while different cells within a same area are separated by dotted lines. It is perhaps more easy to spot on the larger-sized puzzle (which you can see by clicking on the image).
Due to the size and a few very slightly tricky points (not tricky enough that I’d call this puzzle hard, but tricky enough that they’d give a beginner a bit of a pause), I’d recommend a complete newbie do some of your smaller puzzles first. However, it was very satisfying, and definitely one that a solver with moderate experience could do. 🙂
Also, inb4 TheSubro’s inevitable pining for the “real” MellowMelon.