There were many with interesting premises that utterly died. The idea was there, but it never seemed fully designed or put together. Or, the premise was referenced, but never really developed or integrated.
It's the main problem with Ren'Py.
Globally speaking it permit to do as much as Unity ; I say "globally speaking" because, while it's true in theory, in practice there's a limit due to Python being not only a script language, but also one of the slowest.
This "near to no limit" base lead a lot of devs starts with big ideas, having seen them in more professional games. But then, they hurt the knowledge wall. Yes, professionals can do this or that with Ren'Py (like Winged Cloud that, 6 years ago, put old school 3D dungeons in
Sakura Dungeon), but they are professionals. Therefore they know how to do it, and their code will be hardly understandable by pure amateurs.
And this also apply to more basics game mechanism really. The author of
Pact With a Witch struggle since two years with his interactive sex scene. Basically, you click on a body part, choose one of the action that pop-up, and some computation with a bit of randomization will give you a result shown on the screen ; do good enough for long enough, and the girl will climax. It's something that Flash games already had in the 00's, and not too difficult to implement... if you're a programmer. But if you're an amateur like him, there's a lot of small bugs that stack and are difficult to identify and solve.
To this, is added the lack of knowledge regarding Ren'Py languages. There's the example of the
show
/
scene
above, but the most significant is the "blocking screen" used for free roaming.
One day, a dev that haven't read the documentation, found a way to do this:
Code:
label whatever
show screen Whatever
pause
jump whatever
But there's a lot of contexts where this will break the game, or make it really difficult to play ; a quick look at the documentation would have shown that
call screen Whatever
do what the dev wanted to achieve.
And now there's way to many devs who are doing the same, because they saw it "done this way" in another game. But like they don't know why it's done that way, and that is should be done otherwise, they also don't know how to solve the issue when people start to complain that it don't works, or that the game have a strange behavior.
All this being multiplied by 1000 since Ren'Py have a really big base of users, and therefore tons of "ready to use" code, easy to find, but hard to understand, harder to adapt to your particular situation, and near to impossible to fix if you don't have a codding background.
Most of unfulfilled promises with Ren'Py games come from this.
The dev saw it, tried it, found a problem, and never found how to solve this problem. And like they face the issue in real time, instead of developing the whole game mechanisms before they even start to write the game itself, they just drop the idea ; "sorry, but in fact I don't know how to do it". Except that they don't say that, they just expect that the players will forgot about their promises.
Engines like Unity encounter the same kind of problem, with a small difference that change everything.
While there's also a large base of users, and therefore tons of "ready to use" code, you rarely add game mechanism on the fly. The nature of the engine make it that you generally start by creating the game structure, what mean that you'll see if you effectively can do it before you even start making promises.
Plus, it's an engine more professional, therefore many amateurs don't use it, fearing that they'll not be able to use it.