Star Fox Assault for the Nintendo Gamecube was a worthy addition to the series. The graphics and music are outstanding and the voice acting is mostly improved from previous titles. There are some minor quibbles to make. The game could stand to be a bit longer and the on-foot controls could be better (turning around while on foot is an agonizingly slow process, especially in the multi-player). Still, the game provides fast action and lots of variety. The last mission in particular is incredibly intense; pure Star Fox.
The best part of the game may be the plot and character development. The telepathic Krystal adds a fantastical element to the science fiction. Her relationship with Fox McCloud is developed (one wonders why a character like Fox, who has killed thousands of people/creatures in battle, acts so embarrassed when confronted with the issue of romance).
Also of note is the relationship of Fox (an orphan) with several de facto father-figures. He becomes very protective of his aging mentor Peppy Hare. Fox also has a strange relationship with Wolf O'Donnell. The older Wolf claims to hate Fox, yet repeatedly saves him. While not exactly on good terms with Wolf, Fox has some level of admiration for him and takes his advice to heart. It reminded me of the relationship between Amsterdam and Bill the Butcher in Gangs of New York (right down to Wolf's missing eye).
Finally new villains are introduced, the Aparoids. They are partly- mechanical insects. Many have compared them to the Borg from Star Trek, but I feel they owe at least as much to the Formics (or "Buggers") from Ender's Game by Orson Scott Card. Either way, they are a distinctly non-mammalian form of life, and as such inspire a fearful reaction.
A great gaming experience overall, I highly recommend it.