They're not only adorable but both do a fantastic job of setting up their personalities without needing to say anything. Your cartoon version of Luigi looks to be a kind, humble fellow ready to lend a helping hand while your cartoon version of Mario has a more confident and daring appearance. Overall, it's a really simple piece of art, sure, and you could have given them something to do outside of existing in a white void but I am a sucker for expression. If I can form an idea of what this version of the Mario Bros is like, then I don't really need that extra stuff included in the piece, do I?
If you were to design Peach outside of DiC entertainment, would she still go by the name "Princess Toadstool"? Would she still have tan skin? Would she still love Milli Vanilli?