pure smut just is way too restrictive to ever be properly great, imo.
If you only limit yourself to one market, sure. I recommend Takamakuran's "A New Game" (yes, an incredibly easy to search title, I know) which has been
uploaded to F95zone. It's a JRPG with a solid plot, legible translation, and excellent scenes--and most importantly, it's complete. The artstyle might turn you off a bit, but pretty much all the reviews say that it grows on you really quickly.
For a more mainstream (read: well known, A New Game is actually super vanilla as far as kinks go) choice, the illustrious Monster Girl Quest (which I recently completed for the first time myself) is highly regarded for its
writing. I'd slap a warning about its tags, but considering we're most likely CoC veterans here, there's really nothing that extreme. If you're like me and the weirdest kink you have is something low-tier like anal, you can turn off vore scenes--as it is, the majority of the scenes are entirely optional and viewed-on-loss, and the ones that
aren't optional are pretty vanilla. Just some light femdom and vaginal sex.
Fair warning though, the art quality jumps all over the place since the creator commissioned a whole bunch of different ones for his circle. That means you can have some really nice designs one moment, and then you'll want to gouge out your eyeballs the next. Alas.
But hey, you asked for good writing in a porn game, here you go. It's probably one of the most well-known examples of it, too.