Is it as good as 999? No. In almost every area, no. But it's still a great time. Except for two things: Those character models never get easier on the eyes. And the dice.
Every Persona game has its faults and this one is certainly no exception. That aside - P5 made the life-sim portion tie into the RPG portion more neatly than 3 and 4. And dang it if that system doesn't get me surprisingly engaged every time I play/replay a Persona game.