How can I describe '666 Satan'? Probably the first word that comes to my mind would be 'typical'. If anyone is looking for a generic, typical shonen series, than this manga is just what you are looking for. However, I suggest picking another title, because this one is a sad disappointment. The main characters personalities are extremely similar to Bulma and Goku from 'Dragon Ball', with a touch of 'Naruto' - ' I will make my dream come true' philosophy. That being said, we can't expect nothing more of them than dull friendship speeches and fights (which, in my opinion, are just average). As story progresses, the title looses it's comedic nature and becomes more serious, however, the plot is so simple and plain that the 'seriousness' can't save it. The thing that tries to save it, but fails, is 'fan service', that we can see a whole lot from about the tenth issue.
The drawing style resembles Masashi Kishimoto style, however, there is a certain problem with characters anatomy (e.g. the arms are too wide or the face is deformed).
In conclusion, I wouldn't recommend this series to anyone. It is simply dull, and it copies schemes from other popular shonen manga. It's better to read them first and leave '666 Satan' alone.