Tooth Trouble is my first experience with both the Ready, Freddy! series and Abby Klein's work in general, and after reading the short chapter book, I'd say I'm neither really impressed nor disappointed. It's rather mediocre kidlit, I suppose; some kids and parents will love it, some won't. Shrug.
The two big complaints that I had were things most people, I expect, will hardly notice. One, the kids really enjoy YELLING SUDDENLY IN ALL CAPS, which drives me friggin' nuts. Two, various Random Things (insults, especially) were often unnecessarily capitalized for little reason. I found it quite annoying, honestly.
Other than that, I'd say the story itself is like a (lesser, honestly) male-protagonist version of Junie B. Jones. If you're one of those parents who decries Junie and her friends as foul-mouthed, aggressive, brats (and I'm not joking; I've seen quite a few surprisingly impassioned denouncements of Junie B. Jones in the past), you're gonna hate this series. Junie and her friends say some childish things to one another, but Freddy and his gang run wild with the taunting. Which, I'd like to point out to the pearl-clutchers, is how many (I'd say most) children actually speak to one another.
So if you're looking for a "first tooth" book, either because your child has lost his or her first tooth or, like Freddy, he or she is upset s/he hasn't, Tooth Trouble might be a good read for you. Alternately, if you think your child would enjoy the Junie B. Jones books, but you find yourself dealing with the "girls have cooties" response, Ready, Freddy! might be a good alternative (especially if you can use it as a stepping-stone to Junie B. Jones--and more egalitarian reading tastes--later).
As for me, I can't say I'm sorry to have been born the decade before these were published; at least with Tooth Trouble, I'm not yet getting the sense that I missed out on anything significant by not reading these as a child. But, of course, I'm certainly not going to swear off the series, and I'll likely come back to it at some point. Possibly soon, depending on what's available at my library.
And who knows? Maybe Klein will surprise me in the sequels.