First off, I am not a big fan of these phone games. Initially an interesting premise, it has been abused by many a Dev. This one promised NTR (netorare) and NTS and the LI looked very cute, so I gave it a go. Suffice to say, I have thoroughly enjoyed it.
What sets this one apart is the visuals and decent writing. It also works on the "less is more" concept. At times it can be frustrating, but it does raise the tension and allows your imagination to fill in the blanks. Oh, there are visuals and even animation, just at times you cannot see a wide angle of it. Frustrating, yes, but it is in keeping with the supposed phone/camera/video aspect of it.
As mentioned, the wife is very fetching. I know that is subjective, but not sure how anyone could conclude otherwise. She has that mix of cute-smoking hot that appeals. You get plenty of pics of her.
There are two storylines as far as I can tell - NTS and NTR. The NTR is not hard cuck - people confuse that all the time. At least in my playthrough, the husband didn't have a lot of agency after a certain point. The train left the station and all he could do is watch it unfold. Very titillating. The NTS is what you would expect and, frankly, more down the cuck road where he is an active participant, from afar, in the planning and execution of the action.
The build-up is just the right speed. By Version 8 - you are really getting into the action. Be mindful, choices will steer you one direction of the other. I found myself going down the NTS route and had to backtrack. No problemo.
So, while I hesitate to throw 5 stars around, I'm giving Stay Online the Full Monty. I think, for the phone cheat/ntr genre, it is worth the 5 stars. Granted, if the tags don't suite you, don't play it. If you like NTR, however, it certainly scratches that itch. Try it out.