Take a look at this question about the difference between 'embarrassed silence' and 'embarrassing silence': http://classic.italki.com/question/361855 In both cases, the distinction is the same: it is a question of cause and effect. The combination of past participle and noun (disappointed look) refers to something that happens BECAUSE the person is disappointed. If I am feeling disappointed about something and I look at you with sad eyes and a drooping mouth, you can tell that I am disappointed. This is the same as the 'embarrassed silence' in the other question - a silence which occurred because people were embarrassed. By contrast, the combination of a present participle and noun (disappointing look) means that the 'look' of something or someone CAUSES disappointment - as in Lee's example of a cake. Again, this is the same as the case with 'embarrassing silence' - a silence which occurs and so causes embarrassment for people. This applies to all adjectives formed from participles. What do you think the difference is between a 'worried look' and a 'worrying look', for example?

I am not sure what you want to know exactly. Perhaps you want to know the difference between the two? I can show you that, at least. "disappointed look" means that someone is showing disappointment on their face. The facial expression giving off that sort of emotion. For example: "My boyfriend gave me a disappointed look when I told him I had to leave for a few days." "disappointing look" means that someone or something is in such a condition that the person looking at the person or thing would feel disappointment. For example: "I am not a good cook, so the first cake I ever made had a very disappointing look to it. I wasn't sure if I wanted to even eat it, because it made me so sad to look at." This is a brief explanation of these phrases, but I hope it makes sense to you. If you have more questions, please let me know.