A nostalgic tone expresses a sentimental yearning for a return to or of some past period or irrecoverable condition.
Indignant is incorrect. An indignant tone expresses anger, especially when the writer is angered by something unjust or unworthy.
Regretful is incorrect. A regretful tone expresses a feeling of sadness, repentance, or disappointment over an occurrence or something that one has done or failed to do.
Objective is incorrect. An objective tone is factual and uninfluenced by emotion or personal prejudice, thus allowing readers to form their own opinions.