Positive words for unexpected

Fits when a phrase such as a happy accident or a happy surprise says the chance turned out well

Not when the event is serious or sad; happy can sound flippant

Fits when the news or the visit was not expected and was gladly received

Not when the surprise was mixed, such as a bill or a hard truth that needed saying

Fits when a kindness or a success arrived that no one had hoped for

Not when the writing is casual; unlooked-for sounds old-fashioned in a text

Fits when a good thing came by lucky chance, as in a serendipitous meeting

Not when the surprise was unwelcome, or it came from planning, not chance

Fits when work or an approach feels new and original

Not when the idea is only new to the speaker but common elsewhere

Fits when an idea, a manner or a style breaks a dull pattern, as in refreshing honesty

Not when the thing is merely different, not better; refreshing praises it

Fits when the unexpected part is a clever new way of doing something

Not when the surprise came from accident, not ingenuity

Fits when a design, a solution or a piece of writing is unlike what came before

Not when the work borrows heavily from a known source

Fits when a call, a gift or an offer came with no warning, in casual speech

Not when the writing is formal, such as a report

Fits when an unplanned act or outing turned out well, such as a spontaneous party

Not when the lack of planning caused problems for others

Fits when a speech, a performance or a gathering was put together on the spot

Not when it was rehearsed and only meant to look unplanned