Game design is all about compromises. When I created Knytt Stories, I was able to create a much larger world, thanks for the simple graphics. With Saira's puzzles, animation, graphics, and sounds, I couldn't extend the play time a lot. We were mainly two guys doing all the main work, me for 6-8 hours per day over a full year, to create that short episode. I really put all my energy and soul into into creating something really good.
Then, of course, it's impossible to please everyone. I made Saira shorter so I could spend more time on atmosphere and graphics in it. Some people appreciated that about the game while others didn't. I've heard people saying that Saira is well worth the money (some saying it's really cheap considering what you get for it), and at the other hand there's people who regret paying for a game that turned out to be so difficult or short. For every game I've released, I've received positive and negative reviews. Of course, the people who turn out not to like it will always feel cheated as they paid for it, and the only way to fix that is either to create a game so good that everybody will like it, or set the price so low that no disappointed person will feel they lost something. Unfortunately, the first option is impossible (I'm simply not that good), and the second option could never support my game development. Also, the website itself only points out the full version contains four more planetary systems, I didn't promise anything else. Perhaps I need to state that more clearly somewhere though. I just put the multiple episode support in the game in case I want to do another in the future, or in case someone else wants to. That doesn't mean I plan to right now.
Don't misunderstand me, I'm sorry that you didn't find it worth your money and I wish I could make it so good that you would enjoy it more rather than feeling cheated, but this is bound to happen to some people everytime I release a game. However, I'm more than happy with the general feedback I've received for Saira, and I think $10 is a good price for it.