Here's the thing with me. I can't criticize anybody for writing fanfic, having written and published six or seven Sherlock Holmes stories, myself. And while I have avoided all the sea monster reboots, I like Scalzi's work and thought I'd give this one a try. I read the Piper original when it appeared back in 1962, but I've also read Ardath Mayhar's Golden Dream: A Fuzzy Odyssey, which I suppose some might label fanfic as well.
But look at it this way: Most of the people who read this book won't have read Little Fuzzy. The vast majority of them weren't born when H. Beam Piper was writing, and I suspect they've never heard of him. If they read this book, maybe they'll be curious enough to read the original or even Space Viking or A Planet for Texans.
As I said above, I like Scalzi's work. I've reviewed his books on the blog, and very favorably. I like his writing style, which doesn't call attention to itself, and I like his pacing and his characters. And I liked Fuzzy Nation.
Jack Holloway, the protagonist, isn't a nice guy, but, like a Heinlein character, he's a competent man, good at just about everything. If you don't count human relationships, that is. He's terrible at those. He's happy to help the big bad corporation rape a planet if it fills his pockets, too (there's a little Avatar in here, I guess). But then the fuzzys move in. Literally. They move into his house. Are the sentient beings? If they are, Jack will lose the huge fortune he's just discovered, but it falls on him to prove that they are.
Humor, rousing courtroom drama, despicable villains, action, and a great dog. All good stuff. If you revere Piper and his memory, not to mention his fine novels, you might want to skip this just because. If you want to read an entertaining SF novel, then by all means give it a try.