Excellent! Probably best in series.
I've played Ace Combat 4 and Zero; great games. Ace Combat 5: The Unsung War, however, brought the series to new heights. This is both a game and a movie. The cut scenes are absolutely amazing to look at and the voice acting brings the characters to life. Gameplay is a blast, even though its still the same Ace Combat formula.
The music in Ace Combat 5 is superb, covering up most of the annoying, corny and sometimes pointless radio chatter and keeping the battle exciting. It would have been nice to see an upgrade to the graphics from the previous title but that flaw can definitely be overlooked.
Unlocking new planes and replaying the 27+ missions for better grades adds to the replay value as well. Another great title for the PS2 library!