I'm reading the Baby-Sitters Club books now, because my girlfriend read them as a kid, and she likes to read them with me. The books have been okay so far. They have some problems, such as lengthy filler segments that are irrelevant to story at large, and the "minor" subplot of Book 3 taking over the entire story.
Fortunately, these problems can easily be avoided in the future, if Ann Martin starts outlining her books ahead of time. Since this series will become her main job, not just a one-off thing, I'm pretty confident she'll put more effort into them.
We're officially stopping at Book 5 (and the prequel), then we'll jump ship and read another series for a while. I'm eyeing the second 39 Clues series, where our heroes are forced to become international criminals to save a series of hostages. If it's as good as the first series, it's worth reading.