Sonny is what remains if you cut away all the elements save the battle system and some story progression from a jRPG. Despite the simplistic approach to gameplay, it’s incredibly fun. Sure, all you do is battle enemies (to get XP and money), chose skills on level ups and buy new equipment. But the game designers have honed these aspects to perfection and made them incredibly addictive.
That said, the difficulty is less a question of strategy than perseverance. If you level up high enough, none of the battles should pose any real challenge, apart from the last few after the official story has ended. The story itself is kinda interesting, mainly for the fact that you play a zombie who hasn’t lost his mind, but his memory. Sadly, at the end the story is merely halfway over (or even less, no way of knowing) and you don’t know much more than at the beginning of the game. There’s a second part, but I fear that one will end similarly halfway.