Graphics: Visual quality is a top notch, from illustration, sd/chibi form, dungeon and skill crest & effect. Art style is family friendly, no excessive lewdness, but still beautiful.
Sound: Full voiced chara, amazing bgm (ex: teikoku senki, overdrive series). Even songs for anniversary events are good.
Gameplay: For me, it's the best gameplay for mobile games. The potential of one finger control is brought to the max. Punicon is great.
Story: The story premise is like romeo & juliet, but it is light & dark instead. There are many side stories too which from every event.
Value: There are only two gacha, character & weapon. For weapon, it's not too necessary because you can gacha with weapon ticket (from reward) or with weapon exchange method, so you can mostly focus on chara gacha. There is no rate up for a specific chara.