Let's get one thing out of the way before I continue; if you have any prior interest in Spy Fox, it's because you played these games as a kid. If you're playing these without any kind of nostalgic background, you won't have the same experience.
That said, however, the first installment in the Spy Fox series seems to disprove the notion that nostalgia is a crap-covered filter. Yes, it's still a kids' game at heart, but it's doused in a comic book art style and brimming with amusing one-liners and real-world references; the majority of which flew right over my head as a kid. Humongous made kids' games that had some damn good writing, and Spy Fox: Dry Cereal is a prime example. It never wanders into subtle adult references the way Pixar does, but the cultural references got many a chuckle out of me.
If anything, the game is too-filled with good writing. The titular character is suave, and his brand of humor is dry as a desert, but he has a habit of delivering one-liners any time he enters or prepares to leave an area. The writing itself never gets grating, but having the game hampered down by dialogue so often, especially when backtracking, can get annoying at times. Also potentially annoying are the puzzles. Most of them, I remembered from playing the game as a kid.
The solutions are by no means Monkey-Island level of crazy, and you won't be doing pixel-hunting, but your hand is never really held as you progress You space out during a cutscene and you've got to do a bit of memory recall. Not to mention, I have no idea how a kid could figure out some of these puzzles.
However, these are minor complaints. Spy Fox isn't a "hard game", and even if it slows down every so often to deliver oddly-choreographed dialogue, you're not going to grow increasingly impatient with it. The art style is fun, the writing is mature yet still kid-friendly, and the game's collective parody of spy culture is refreshing and appreciated. Heck, even if you didn't play this as a kid, it's still worth a shot.