When you eat something and you think it's tasty, please don't hesitate to express your feeling especially someone cook and serve you.
Even if they said "It's not really tasty, is it?", but everybody love to hear positive comment like saying 'yummy' about their food.
Elementary Level
It's not difficult to say "delicious" in Japanese.
おいしい
Oishii
or
うまい
Umai
Delicious
If telling someone in a polite way, just add "です" behind.
おいしいですね
Oishii desne.
or
うまいですね
Umai desne.
It's delicious.
And you can also add "very" or "awfully".
とてもおいしいですね
Totemo oishii desne.
It's very delicious.
or
すごくおいしいですね
Sugoku oishii desne.
It's awfully delicious.
Advance Level
Following are other expressions:
なにこれ超おいしいんだけど *casual way
Nanikore, choo oishiin dakedo.
What's this... it's super yummy.
くそうまいなこれ *casual way
Kuso umaina kore.
This is damn good.
死んだじいちゃんにも、食べさせてあげたかった
Shinda jiichan nimo tabesasete agetakatta.
I wish I could let my grandpa who had died to eat this.
