Rich is used to describe foods or flavours that are considered very good, but unpleasant in large quantities. e.g. the first cake was light and fluffy. I ate the whole slice. The second cake was very rich. it was thick and heavy, and although it was delicious, i could only eat a few mouthfuls.

Thank you Phil. :)

Like Neil said. Also, note that rich food tastes good because of fat and / or sugar content, and is usually used to talk about deserts. The word "rich" is very useful if you need to decline a desert that your friend made. "Another piece? The cake was so delicious, it's just a little too rich for me" (then, you can indicate your stomach to show you're on a diet). To talk food other than desert, the term "savory," which has only positive connotations, can be used. Of course, you can use the word "delicious" to talk about any type of food.