There is nothing wrong with the grammar of the above sentence. Americans just don’t say it; I don’t think any other native English speakers (Britons, Australians, Canadians, etc.) say it either. It just sounds strange. (In case you are wondering, “Is it delicious?” is the direct translation of what Koreans ask someone who is trying a new food.)

Part of the problem is that “Is it delicious?” is a yes or no question. It’s too direct and there aren’t a lot of options for an answer.

So, what should you say? Americans usually say:

How do you like it? (or)

What do you think?

These questions are preferable as they are less direct and give the eater many more options for a response. The answer is up to you.