おいしい ( Pronounced Oye shee ) , is Japanese for delecious . I'm not familiar with grammar though. Also お茶 ( pronounced Oh Cha ) , is the word for Tea.

"really good" is "とても良い（Totemo ii）" "This tea is really good!" is "このお茶はとても良い（Kono otya ha totemo ii）".

本当においしい ですね。

You can either use とても if the sentence is formal Ex: このお茶はとても美味しいです！(美味しい- oishii, is the word for "tasty, delicious) Or めっちゃ in informal sentences Ex: このお茶はめっちゃ美味しい！