I feel like the topic is too subjective to be meaningful. Here are my reasons:
1. Many people buy ukes sight-unseen, and develop expectations based on reviews, or appearance, or reputation. Then they expect the uke to be life changing, and are disappointed when it's, you know, just a uke.
2. "Good" isn't a universal measure. The Farallon mentioned above is a great example. My Farallon is a fantastic sounding uke. I first played it at a music store and loved the tone, and then went back and played it for a long time, to make sure it wasn't just infatuation. But up above we have a player who found it disappointing. Which of us is right? We both are. By the same token, I have owned ukes by two incredibly well-regarded makers that many would consider "grail" ukes. Neither of them did a thing for me, and both were sold. In both cases, the new owners were thrilled by their purchases, and one of them has posted frequently here about finding the "one." How could ukes I found disappointing make other people so happy? That's why I don't post the makers; why start a "brand x is disappointing" thread when obviously the "disappointment" is about my preferences, not the instrument itself?
3. I have found that my favorite instruments are ones that I live with, play often, and discover what I need to do as a player to make them sound their best. Often, "disappointing" instruments are quick-lifted at music stores, or purchased online and sent back after a few days. I'm not saying a bad instrument will suddenly sound good, but familiarity can often bring out the best in an instrument. A good example for me was Hofner basses. I never like the look, and felt the violin bass was too closely associated with Paul McCartney to be something I'd want to be seen playing. A lot of the reviews I read of Hofners dismissed them as one-trick ponies. But a couple of years ago I was playing bass in a band and was looking for an extremely lightweight bass that I could play when I started having some back problems. Hofners fit that description, so I gave them a try. At first I was unimpressed, but I gave it some time and found the style and attack that made them sound great. Now my Hofner bass is a go-to instrument, expecially when I want more of a stand-up bass tone.
And finally, sometimes we have to admit that "disappointing" lives in our hands, not the luthier's. I took banjo lessons for a while from Tony Trischka, one of the finest players in the world. At the time, Tony was playing a custom Stelling Sunflower (a *very* pricey banjo) and I was playing an inexpensive import Fender. Tony's banjo sounded fantastic, of course, and mine was sort of plinky-plinky. At one point, Tony wanted to show me something on my banjo, so we swapped for a bit. Shockingly, Tony's bazillion dollar banjo sounded awfully average in my hands, while my cheap import sounded pretty damn impressive in his.