なかなか

なかなか has two uses, depending on what follows.

With a negative, it means something doesn't happen easily, despite waiting or effort: バスがなかなか来ない, "the bus just won't come"; 日本語がなかなか上手にならない, "my Japanese just isn't improving".

With a positive, it means "quite, pretty", better than expected: この料理はなかなかおいしい, "this dish is pretty good". It's a mild compliment, and from a superior it can sound a bit condescending.

Before a noun, it's なかなかの: なかなかの人物, "quite a character".

Compare 全然 (not at all), which is absolute, and あまり (not very). なかなか〜ない implies you're waiting for it to happen.