So, personally I'm a fan of your game's use of real porn and think it's used appropriately. That said, some of the common reasons I tend to dislike it in other games include:
- Drawing porn is hard work. Because of this, games that rely on drawn porn (not CGs taken from hentai games, but drawn by the creator) have to rely a lot more upon sex scene writing and dialogue than they do on images, which basically guarantees that there *will* be sex scene writing and dialogue. On the other hand, a lot of real porn games have sex scenes that go "Fuck her" -> gif of a blowjob -> gif of doggystyle -> gif of a cumshot -> scene over. I personally don't find sex scenes to be hot at all without writing, although some people don't care about that sort of thing.
- You're limited by the type of porn available. This can lead to the context of sex scenes feeling pretty contrived because it's necessary to fit the model's content; "oh, let me just change into a different set of clothes and then we can fuck". In extreme cases, you get ridiculous shit like "oh, this is a sex tape of Girl A, but from a year ago when she had blonde hair and smaller tits". It breaks suspension of disbelief. Again, personally I find context pretty important to enjoying sex scenes; not everyone does. It can also just limit the secenes you get: the main girl in Tales of the Drunken Cowboy uses a model who doesn't have any hardcore scenes at all, and so she hardly ever actually has sex in the game except sort of offscreen, which I found to be a huge dissapointment.
- It's often stylistically jarring - obvious differences in style between different characters / different shoots, or it doesn't match the aesthetic of the rest of the game. Pretty much any hentai image fits well with the RPG Maker aesthetic ubiquitous in japanese games.
- It's often lacking in character. Pretty much every porn scene except a really specific, like, fetish shoot or something, has the girl look and fuck like a porn star. This is fine if the character in the game really is a porn star, but what if they're an innocent, shy virgin or a brash tomboy or an emotionless robot girl or a haughty bitch being blackmailed? Your average cheerleader-themed real porn movie features a 28-year-old woman in a cheerleader outfit who unconvincingly says a couple of sports-game-related lines before discarding the act faster than she discards her clothes and fucking like a Times Square hooker for 20 minutes.