It’s of no interest to me when he’s a contemptible ass with no redeeming qualities whatsoever who doesn’t behave like any human being ever would.
The sexing up doesn’t bother me so much in and of itself; it’s the fact they want it both ways. They want to say sure, it’s totally gross and he can’t look at his sister like that because she’s only 11, blah, blah, blah, we’re not taking this seriously, but they’re happy to throw in the panty shots, the bath scenes, the psychological reaction played for laughs, and on and on. I can take kink - I enjoy …monogatari shows; even the toothbrush scene and the ancient-vampire-who-looks-like-she’s-10 and all the rest of it in that franchise don’t bother me that much. It’s problematic, sure, I could see some people getting really upset over it, quite possibly rightly so, but there’s some effort gone into making it an actual part of the narrative and to have it provoke more of a reaction than just hurhurhurhur underage bewbs. There was nothing else to No Game No Life’s fanservice in those first two episodes other than that. I like actual wit, intelligence and emotional complexity to my otaku-bait, thanks - I didn’t see nearly enough of either in that show to make it worth watching any more.
As far as insufferable protagonists go Death Note was just as bad, sorry. Again, I’ll argue until I’m blue in the face that you’re supposed to find both male leads in Death Note totally cool, just in different ways (unrestrained power fantasy, dreaming of getting revenge on everyone, putting the world back the way it’s supposed to be - kooky idiot savant with zero social skills who doesn’t have to worry about fitting in with society because he’s just that awesome he can make society fit around him). Both of them are painfully obvious archetypes, none of their failings mean anything significant* and/or they’re rendered irrelevant by plot armor. It’s a tissue-thin idea that substitutes idiot psychobabble and fanservice for anything remotely meaningful. Christ, at least I got frustrated over No Game No Life because it actually made me feel it could have been a pretty good show, if it had been written for any other reason than to make career shut-ins feel better about marrying their hug pillows. Death Note just seemed like it was always going to be a lazy Holmes/Moriarty riff with a silly supernatural twist it was never really interested in exploring beyond STOP ME BEFORE I KILL AGAIN.
*I mean, they never do, right? I actually quite liked God’s Memo Pad, there’s a good example - it wasn’t a bad show, but if you think that “hacker” was anything other than moe nerdbait you’re kidding yourself. If you spent all your time shut up indoors in front of a bank of monitors and lived off ramen broth and regular Dr. Pepper you’d be dead in short order, not a cute/sexy pseudo-autistic genius girl. L is the exact same thing. His weird tics, habits, isolation etc. serve absolutely no purpose other than to get fangirls excited and fanboys laughing at the freak, end of story.