Although the triangle was left open-ended, I was still pretty satisfied with the ending. It leaves room for future development between Alto, Sheryl and Ranka. I'm sure that Kawamori, being the master troll that he is, was a bit more creative in selecting the word "Frontier" as the serie's title. Like Sheryl and Ranka said in unison at the end, this is only just a beginning.
Plot-wise, nothing was particularly definitive, with the exception of the human-Vajra connection. Grace could still be out there somewhere with her accomplices planning their next move. Our train-loving Zentran still hasn't found who he's looking for. If anything, maybe the continuation will even involve Macross 11 and Earth.
Being optimistic, I look forward to new adventures from the Frontier universe. The ride's not over yet
