I prefer art in NTR games where it looks as attractive and bright as any vanilla eroge so you can feel the same sense of forging a relationship with a heroine which would normally lead you to her route and the whole happily ever after thing. Up until the NTR happens. Especially with the heroines drawn just a cute and pure looking as they are in typical vanilla games. Much better than dark and gritty art.
The only thing I insist they change from vanilla games, is the perspective in the sex scenes. Too many artists doing NTR games draw the CGs the exact same way as in other games, with it showing just the heroine and very little of the guy doing her, usually from an angle that makes it look like you're seeing from his eyes. And that really throws things off in NTR. In NTR you're supposed to be taking the protag's PoV, so if the heroine is having a sex scene with a different guy, they should draw it from a third party PoV. It makes all the difference. I know not every liked their new game, but
mekujira understands this well. Any NTR scenes in their games are always drawn from a third person PoV and it always fits the feeling of proper netorare. Still, I can understand why they stick with it in most stuff. Most artists are just used to it, it's harder to have to draw most of the male body too and not the mention it'll allow anyone who prefers netori to easily self-insert into the guy stealing the girl instead. Still, I play NTR games for netorare and prefer them to do it properly.
I also like a game to have a 'good ending' possibility, where the protag either prevents the NTR or gets the girl back in the end. But I think you should have to work for it. I find it hard to really sympathise when you have to make bad decisions for the NTR to happen, whether it's to do something obviously stupid, totally neglect the girl or all but drive her into the arms of the other guy. For me the best NTR is when the protag has tried to do everything right and still gets betrayed. He doesn't have to be perfect, he might make a few mistakes without realising he's causing her to drift away from him. He might just be too nice and considerate of her feelings while she actually wants him to be more assertive and keep pushing, rather than backing down the moment she shows a hint of resistance. In any case, it should be a mistake a guy could easily make. That way you feel the same sense of betrayal, unfairness and loss as he does. In other words, the choices are divided between good choices and dumb ones, but between things that might seem right from one perspective or not from the other. And if you make any wrong choices it can trigger the chain of events that lead to NTR. If it an NTR game, then NTR should be what happens almost every time. You should have to be careful and work hard if you want that happy end, I get quite disappointed when game do the opposite and gives you the happy end so long as you make one or two good choices and you have to all but sabotage his relationship with the heroine to get the NTR to work.
That's all I was thinking. Not replying to anyone specific, just my casual thoughts.
Shine