I'd argue that finding the endings unsatisfying is part of the point of the episode in terms of how it seems to be both a love letter to, and a criticism of, interactive narrative. The obvious criticism is simply spelled out by Stefan in the 5 star ending when says that his mistake was trying to create a game with real choice instead of the illusion of it.

This is a reflection of the piratical reality of making these kind of narrative, mainly that you can only afford to make a given amount of "parallel content" so you quickly rail road players down the same path while pretending they've had a say in the direction they're going. But so long as the player know which choices mattered and which choices didn't, or what other combination of choices would have gotten the same ending, it doesn't really matter. Hence why that version of Banderstatch was the best reviewed.

However problems start to creep in when people go over the narrative multiple times making diffrent choices. You quickly find out which choices matter, and how much, which are window dressing, and how drastically diffrent paths all end up merging towards the same end points. Ending that suddenly feel a whole lot less satisfying when you realise it largely didn't matter what the characters did to get there. And, as you point out, you quickly get bored of the content in-between as you repeat it ad-nauseum to head down the diffrent paths so that when you do get to another ending it's inherently less satisfying than if it had been your first.

All in all then it's almost always best to simply go through this type of narrative once.... but that's simply not how people consume them because people are people and they are always going to want to know what they missed out on. I know I do, for example I loved Fighting Fantasy as a kid but you show me someone who played those books with out keeping their finger on the last page and I'll show you a lair.

This is an attitude the show obviously understands and embodies in Colin "wrong choice", "he's just exploring all the paths", "which ending did you get?" "all of them" etc. and it can be seen in how it's constructed, how it doesn't actually end on most endings and how it speeds over recaps early on before just skipping you back to the obvious branch points. It's all designed to make sure you replay at least some of it so you start to see the seems so you understand that they, just like Stefan have only really given you the illusion of choice. All of which inherently undermines any impact the individual endings have.

The point in other words being how the way people consume interactive narratives has a tendency to undermine them as any given version of their narrative because of how inherently artificial their construction has to be in order to be practical.

But being constructed in way to result in being deliberately unsatisfying is still to be unsatisfying what ever way you cut it. I just don't think there's much they could have done story/ending wise that would have stood up to how the vast majority of people would have ended up watching it. So reflecting that fact in the episode, even if it was at the expense of the story itself, is at least a very Black Mirror thing to have done.