Aside from the avalanche of other bugs, (don't they test this crap before releasing it?) the main issue was that for a time it wasn't possible to login to LJ at all. And when users were finally able to log back in, (Unfortunately, both LJLogin and Juggler are still functionally useless at the moment) many users noticed a few problems. Serious problems.
It's bad enough that random people might be able to read friends-locked or even private posts, but a security glitch of this scope is criminally inept.
Edit: Incidentally, here's the thread detailing most of the issues that everyone's been having. Aside from the chorus of "Stop 'fixing' thing that aren't broken!" and the usual complaints about LJ's 'customer service' (or lack thereof) the thrust of the criticism is that these changes pretty much render LJ functionally useless.