A pretty fantastic slave breaking experience, bit of a learning curve. I got about 20 hours into it and just got to the point where I could train disobedient slaves to high quality efficiently, but still have no idea how battles or racing really work, and it seems like there's a huge amount of late-game content that I haven't yet gotten near.
I'll start with some advice for new players who might be interested, that I learned through trial and error. First, unlike other slave games, your PC is super important - his stats determine the effectiveness of his training. So if stuff isn't working, it could be because your PC's skill in that area is too low. Also, obedience is primarily affected by some combination of mood, fear, and previous obedience/rebellion. Every action that is obeyed, therefore, increases future obedience - and every action that is disobeyed causes rebellion which must be overcome with increasing fear. However, increasing fear usually also decreases mood, and ending the day with low mood can cause despair (depression) which will lower the mood at the start of the day and is harder to get rid of. Therefore at the start you want to increase mood and fear, and then get the slave used to doing basic obedience with easy tasks like gymnastics or tidying, before moving on to other trainings and sex.
Ok, but how do you increase mood at the start without also causing "spoiling"? Well, there are actions that increase mood but have nothing to do with spoiling - in fact spoiling only is related to not having enough rules, giving too many privileges (like sleeping in your bed before a certain devotion threshold), or giving too generous of rewards for meritous slave behavior. Therefore encouragement, taking your slave to the spa for the $3 spa treatment, giving them drugs/alcohol and letting your slave clean herself are actions that you'll probably have to repeat early in the game to keep your slave's mood up, to get your slave to obey, before your slave starts excelling at things, upon which you can give rewards that improve mood instead.
Other than that, giving your slave a sundress and shoes will improve mood, and paying attention to the slave's uniform when doing specific trainings (Frilly Apron for cooking etc) are helpful for ensuring good performance that you can then reward.
I'm guessing there's also a way to play as a really brutal slave trainer that uses a lot of torture and fear, but I haven't explored that so far.
Last advice: feel free to be picky about the slave you end up training - some combinations of stats just aren't worth the trouble. Haughty and Feeble are particularly bothersome, I avoided trying to train them.
As for the review, the portrayal of the slave's internal psychology is fantastic. Once you get the hang of it, the right decisions to quickly and efficiently break a disobedient slave are slightly different every time.
The sex scenes are well written and the image quality is decent, although there is usually not as much specificity to the images in the training scenes and the characters - in SlaveMaker3, when you trained Belldandy, all the training images were distinctively Belldandy. In JoNT, more often, generic images or images that only match the hair color of the slave are used.
Finally, if I were to give advice to modders / developers, I'd ask for a content selection mod - scat, watersports, gaping, bestiality, cannibalism etc not only all feature in this game, they are often unavoidable in the course of training. For me these are huge turn-offs and I'd love it if we could control the content to avoid these things.
Second, some more "unique" slaves would be nice - kind of like girl packs used in Brothel King, or the named slaves in Strive4Power, or the majority of the slaves in SlaveMaker3. Let people make post custom-made characters, with images, unique dialog, maybe give them quests and stuff.
Lastly, I wish there were more ways to have sex with slaves outside of Active Sex and the three generic "relaxed" and "rape" options (vaginal, anal, and blowjob). I'd love a "relaxed titfuck", a "relaxed doggystyle", "relaxed bondage fuck" etc.