Como dizer "nada mal" em inglês

*Adding:

(something) is not half bad

This is a casual way of saying that something is quite good.

This is an example of understatement. What you really mean is "This is really good!" but you say "This is not half bad" instead because:

you want to seem relaxed and not too easily excited
you want to emphasize how good something is by understating it in a funny way
you just want to express your feelings in an unexpected way

You can use this expression in all kinds of situations, but it's most common in casual spoken English.

FONTE

wow... lembro que essa foi uma das primeiras expressões que aprendi.