This game makes all the correct motions of a trainer, without truly being one. Let me explain.
There are, fundamentally, two subtypes of training games. A game of the first type lets you navigate a system of mental stats and lead the girl on a path to enjoying sex—that is considered a win—or to mental breakdown of some sort—that's a defeat. The second type of a training game will make you jump through some hoops, rewarding you with a preconstructed narrative of a path to success piece by piece. Several paths to success if a dev is ambitious enough. To simplify, you have sandbox strategy games, and visual novels with extra bells and whistles used to hide the fact which is: these games are visual novels.
Princess Tower is, sadly, just a visual novel with bells and whistles. But at the very least, it's good at pretending. Unlike countless soulless imitations, Princess Tower has proper trainee stats, such as submissiveness, sense of fairness and, most importantly, infractions. The core mechanic that drives the narrative is that you can't punish your ward or solicit some lewd action just because you want to, you perv. No, here you need a reason, you need her to transgress somehow. Only then you may administer the spanking. But, as I said, it's a rather superficial system, all stages are hard locked.
That said, writing saves the day here, as it's very carefully constructed, with witty dialogue and really good characterization, both of the girl and her corruptor. Extra points for OC universe with pieces of worldbuilding integrated smoothly without bogging down the main story. In short, it's a pleasant read all around.
Art is pretty cute, and expressive. I'd peg it somewhat above average. Simple, nicely textured UI. No music or SFX. No hardcore sex yet, not much nudity either (but to be fair, the game does address this deficiency, rather charmingly). Quite short.
For what it's worth, it's a Good experience, 4 stars. But it's not the holy grail, the new gold standard of trainer games.
Alas.