Translation:Finally the big surprise had arrived.
"Finally you had arrived at the big surprise" would be "Finalmente había llegado A la gran sorpresa" and ""Finally he brought the big surprise." should be something like "Finalmente (se?) llevó la gran sorpresa", using llevar instead of llegar.
However, my reasons could be wrong, so maybe we'll see if someone more knowledgeable than I can address this issue.
March 12, 2019 - The word order is incorrect for English, which has the subject first, ahead of the verb in declarative sentences. English uses word order in place of endings. Subject - verb - object (if any). For emphasis, you could write Finally the big surprise had arrived.
I have a couple of issues with this: Is the meaning of "finalmente" here supposed to have the meaning of being the last action (al final), or is it an expression of exasperation at having waited so long for something to arrive or happen (por fin). Because it's not all that clear from the context. I entered "In the end, the big surprised had arrived" and it was marked incorrect.
I guess I just don't like this unit at all. You can't directly translate the past perfect in English. Clauses written in the past perfect are dependent and can't stand alone. Saying "I had lost a friend" is meaningless without context