It's completely casual and really just designed to be played like that - after all, the core mechanics are to tap gudetama for currency and use that currency to cook and collect... yet more gudetama. Each gudetama has unique voice lines and all are funny and adorable, so full marks for sound on that basis. It offers little else though, and the game has remained largely in stasis since its release.
Additionally, since CyberStep (a highly suspect company with a generally poor reputation) has a hand in this, value isn't particularly good and Golden Eggs (the game's premium currency) are ridiculously expensive. This forces most players to sit through ads to get their Golden Eggs daily, and so value is certainly lacking. I'm tight-fisted with my money and very reluctant to spend on any game regardless, so take my opinion with a pinch of salt.
All in all, I really only played this game because I love Sanrio's characters, and gudetama is no exception. However, I'd be hard-pressed to assume that other Sanrio fans might enjoy this game even if gudetama is their favourite. Very cute, but likely to disappoint - play casually or not at all.