「おいしい」[oi-shee] means "delicious" or "the thing is actively delicious-ing" as Japanese verbs (or what is called an i-adjective in conventional parlance) exude "is-ness." 「うまい」 [oo-mai] is also commonly used to express the fact that something is exuding tastiness, and an exasperated and exaggerated, staggered uttering of 「うまい」 indicates that something is exceptionally delicious. Men can change the pronunciation of 「うまい」 into 「うめえ」 [oo-mehh] as slang and casual talk, with a more brusque and rugged feeling that also indicates something is quite tasty. A more formal way is to say 味覚が良い （みかくがよい）[mi-kaku-ga-yoi] which means "pleasing to the sense of taste" or "the taste sensation is great." To rely on an onomatopoetic expression, one can say 「しっかりした味だ」 [shik.kari-shta-ah-jee-dah] meaning "[it is] a robust flavor, it is tasty."