なかなか (or 中々（なかなか） in kanji) is a 副詞（ふくし） (adverb) in Japanese that is frequently translated as ‘very’, or ‘considerably’. It is regularly paired directly with other adjectives, or before nouns (with の coming between なかなか and the noun).

• ここのラーメンは中々（なかなか）美味（おい）しいね。
  This ramen shop is pretty good.
• ミムラさんもなかなか可愛（かわい）いよ。
  Mimura-san is very cute.
• あのシェフが作（つく）るパスタはなかなかの物（もの）だ。
  The pasta that the chef makes is very good.
• 元（もと）カノはなかなかの美人（びじん）でしたが、性格（せいかく）が悪（わる）かったので別（わか）れました。
  My ex-girlfriend was considerably beautiful, but her personality was bad, so I broke up with her.

なかなか can also sometimes have the nuance of being something that is 軽視（けいし）しがたい. This basically translates as ‘difficult to dismiss’, but is a bit closer to English expressions like ‘nothing to scoff at’, or ‘not to be taken lightly’.

• なかなかの事（こと）をしてくれたな。こんな事（こと）をお客（きゃく）さんにどう説明（せつめい）したらいいんだ。
  You have done something that is difficult to dismiss, haven't you? How am I supposed to explain this to our client? (What you did cannot be taken lightly. How am I supposed to explain what has happened to our client?)