Fuzzy Nation is an interesting concept. Scalzi's book has the same characters, and is basically the same novel as Little Fuzzy, H. Beam Piper's award winning novel, just re-imagined and retold. Think of it as Little Fuzzy 2.0
I have read Little Fuzzy and its sequels, including the well done book by William Tuning. Its interesting that Scalzi did not do a sequel or another book with similar aliens and similar events, but with his own characters.
Scalzi, I would guess, if asked would state that his novel, his retelling of the story, is a little more realistic about the actions of some of the characters. I will not give anything further away.
Its a quick read, and well written, yet just because its more realistic is it better.
If I had to say, I would say the original, even if more saintly, was a better story, but that Scalzi, writes a story that is more adult.
IN Scalzi's forward he states that he hopes that a new generation goes back and reads Little Fuzzy by Piper. We shall see.