Good almost in spite of itself.
There are an amazingly diverse set of problems with Star Fox Adventures. There's nothing wrong with having a story that is only there to contextualize gameplay, but Star Fox Adventures promises an epic tale before becoming nothing in particular. Its combat boils down to three different attack combos that work against virtually all enemies, which seem to come in varieties of highly annoying and easy-to-run-past. The puzzles are inanely simple, and usually involve simply spotting a switch. Puzzles do improve towards the end, but even then, they feel about as difficult as the puzzles at the start of the game should have been. There is a lot of backtracking throughout the game. Star Fox Adventures tries to compensate through Metroid-style sub-sections that only open up through gaining new abilities, but there's not nearly enough of this content to make the backtracking remotely interesting. Most of the upgrades are uninteresting, anyway. The most entertaining part of the gameplay, the traditional Star Fox levels, are short in length and quantity. There are a variety of mini-games, but none of those are particularly deep, either. None of this is challenging in the slightest, with the exception of one or two of the mini-games. For those that like to nitpick, this is your game. It presents a diverse set of design decisions to pick apart.
But this diversity ultimately saves Star Fox Adventures from mediocrity. You'll be forced to engage in a timing mini-game to defend yourself against oncoming attackers, shoot explosive projectiles at various targets using a turret and dodge fire blasts while holding an explosive barrel, among other things. The game is so good at making you change your activities frequently that you'll hardly notice how inane each individual part is. It may be a cheap way to disguise how shallow everything is, but it works. Never more than to make the game mildly entertaining, but mildly entertaining nonetheless.
The gameplay, however, is just a means to keep you progressing, and thus, exploring a fascinating world. Dinosaur Planet is a varied and beautiful place, filled with all sorts of visually and aurally captivating objects, architecture, friends and foes. Though the game is several years old, the art of the game has let the game's visuals age well. The sound is just as good. The music is rich and pleasing, but the real star of the game is the voice acting. Fox in particular sounds great, and all of the characters sound exactly as they should. It's unfortunate that such talent was wasted on such a shoddy story, that has only a surprising plot twist going for it. But individual cut-scenes are engaging simply for the quality acting and strong sense of cinematicism, so you won't mind watching the dead-end tale unfold. Being on Dinosaur Planet is a rich experience, and single-handedly saves Star Fox Adventures from the forgettable footnote that it comes so close to being.
Star Fox Adventures will disappoint many people, though it's not an inherently bad game. It lack the depth of better action-adventure games, and is not enjoyable for the same reasons as a Zelda. But for Star Fox Adventure's constantly changing gameplay, and a world that's worth exploring, the game is a nice trip that you won't mind taking once. And for students of gaming, it is a fascinating study on how to cobble together a series of individual design failures into a successful whole.