Interesting discussion...
I guess it depends on what you personally look for in games, and what you expect to get out of them as a result. To be frank, and these are general comments, I don't play games to feel frustrated, irritated or unsatisfied at their conclusion. Like most, I get enough of those feelings in real life. What I imagine most people look for in a game is something that challenges them, and then rewards them when they best that challenge. It's a standard ploy which is ingrained into our behavioral psyche from a very early age. Take your medicine and get a treat, eat your greens and get a nice pudding, do your homework and get to go out with your friends, etc, and so on. And with games we expect it to work that way as well, because most do. And, besides, why would you play the game if it didn't? Reward is what ultimately makes the entertainment enjoyable and fun, and a pleasing distraction from real life woes. It's the challenge and reward system that keeps you going, and brings you back to experience that feel good factor again. If you don't get rewarded for your efforts or, at worst, get punished for them, you naturally question the reasons for even taking on that challenge again. That's perfectly understandable.
Some people may say that it's the journey and not the destination that is important. Personally, I think that's nonsense. After all, you could have the most wonderful drive through the countryside on your way to the coast. But if your car caught fire on arrival and left you stranded there, any thoughts of how good the journey was would quickly evaporate. On the other hand, if you had a terrible journey, but your destination was wondrous and fulfilling, it would all be worth it. In essence, 'last' impressions count when it comes to experiences. And entertainment experiences are no different.
I think an important aspect of any game writing is to ask oneself; is the player going to enjoy this? If the answer is, 'I'm not sure', or 'maybe', or 'I think so', or worst case scenario 'I don't care', then it's probably worth re-evaluating how you proceed. After all, you are writing for game entertainment purposes, not the Booker Prize or Hugo Award.
Entertainment is about providing people with an enjoyable experience, not a miserable one. Yes, you can play with people's emotions during the course of the story, and make them happy or sad along the way. But, irrespective of that journey, a potential destination should be an enjoyable one.
Good endings are cliched, that is true. But they're cliched for a reason. Because they are popular.
Trite it may be, but people prefer 'happy' for some reason.
Games, being interactive, have a distinct advantage over other story-telling media, inasmuch as you can allow for good or bad results based on actions and decisions. With this in mind, I feel that there is no fundamental reason why 'happy' cannot be included as an option somewhere.
After all, destinations are the reason we travel in the first place, and most people prefer a pleasant one.
But coming back to Enderal; it's worth bearing in mind that this is an incredible piece of work by some extraordinarily talented individuals, provided to us for free. We are not owed anything, nor do we get to demand anything, and I would not assume otherwise. The above is simply a collection of general observations and thoughts.