Good grades are really subjective.
Seriously you should only care what YOU think are good grades as long as it gets you into the sixth form/college and uni/other course which you want to do. If you wanted straight A's then sure, you'll be disappointed. If you wanted straight D's then you should be elated! It really depends on who you are. For example my strongest subject is english and so for me getting a B is really disappointing - but people get really angry when I am upset about that because they think it's amazing - for them maybe, but personally I don't think so. On the other hand, I have much lower expectations in other subjects than in English, so wouldn't mind - its all down to you and your strengths and weaknesses.
The only grades which are pretty objective are:
Getting straight U's is bad.
Getting straight A*'s is good.