Ridiculous fanservice is fine in a comedy that's clearly about ridiculous fanservice. Or a hentai game, where that's why you're playing.
It's slightly tacky to take what is, as far as I know, a 'normal' RPG and implement a mechanic where your female characters level up by taking off their clothes.
(I haven't actually played any games in this series, maybe I'm misjudging the targeting? A gamespot review of the first game suggests it was always a little confusing with innuendo that didn't go anywhere.)