Finished the slave route. Just as the rest of the route, the update had good sex content but was very unfocused and lacked pacing. You're given the option to walk Korra like a dog, but the scene feels like a buildup for something, and not a finale. You can repeat it over and over again, but you get no indication of what the next story step is. Randomly checking the tower gives you the option to ponder life which leads to a hilarious but sex-less ending scene.
The Book 4 slave route wasn't bad. It's just that the other books had much more focused stories (which led to less random guesswork when proceeding) and delivered more heavy-hitting, satisfying sexual progression. Book 3 had an amazing finale where you fuck a tied and gagged Toph in the air where she is powerless, that was a great note to end on.
The sex scene in the blimp felt like a love route scene and the work put in there should have been saved for the finale. Book 4 could have ended with the spirits appearing right after we fuck "Korro" doggystyle in the park while she admits to being completely enslaved to you (optionally with a crowd watching so the whole city knows what a slut the Avatar is).
I hope Book 4 love route is about you helping Korra gain back her strength after Zaheer's poisoning in order to defeat Kuvira (who must also be fuckable). I want it to end with a loving fuck inside the destroyed mecha. Or with you and Korra sneaking away to an empty room at the wedding. That would be a satisfying conclusion.