Fair for Its Day: Back when the franchise was still huge, it was actually somewhat praised for its large cast of diverse (at least on the surface) characters.
Older Than the Demographic: Controversially so. The toys feature arguably sexualized teens but are aimed at preteens. It's been critisized for being age-inappropriate. As a result, the characters were eventually retooled to dress more conservatively and put more emphasis on the Be Yourself aesop rather than the fashion and partying.
Overshadowed by Controversy: Outside of the target demographic, the dolls are best known for the controversy they caused about being "ultra-sexualized".
Snark Bait: The hilariously made-up sounding names most of the dolls have. You'll pray that no real-life little girl has them.
The toyline itself is often held up as everything wrong with dolls in the early-to-mid 2000's.
Uncanny Valley: Many comments and jokes have been made about how creepy and inhuman the Bratz look.
Audience-Alienating Premise: Most of the things associated with the Rock Angelz movie and doll-line, the CD included some pretty great songs (Nobody's Girl and So Good) and the video game (also mentioned below).
Continuity Lock-Out: If you want to watch any of the videos, you better start out with the first two (Rock Angelz and Genie Magic) as those two have callbacks to later events and Genie has a sequel called Desert Jewelz. The only ones you don't need to worry are the 2D ones and the Babyz (Super Babyz and Saves Christmas) and Kidz spinoffs. The former because they're a different continuity and the latter, while still the same canon as the CGI ones, don't really have a strong continuity.
The book Will Work For Fashion has Cloe getting a job to buy a dress she wants to wear to her first art gala. This is treated like the worst thing any teenager has ever done because she isn't spending every moment with her 'friends'.
The same book has Cloe (working in a cosmetics shop) mix and match make up of different sorts without her boss' permission. When her boss finds out and fires her, he's treated as the villain.
If we speak of Bratz Rock Angelz, there's Jade saying that if someone was mean to you, don't get mad, just get back at them. And that's not all; they keep talking about how Burdine is going down and how much revenge they are going to commit against her. Sure, she was really mean to Jade at the beginning of the film, but she didn't deserve that much backlash. It makes the Bratz look like revenge-hungry Designated Heroes who refuse to be nice to their opponents (like most child-centered media encourage children to be) who didn't do anything really that criminal to begin with.
The Problem with Licensed Games: A series of video games based around Bratz were eventually introduced. All of these games used the exact same engine and gameplay, had painfully forced tutorials, poor graphics and terrible controls.
Squick: One of the extra clothes one could buy for the Babyz was a small bikini. Another one had fishnet stockings.
Uncanny Valley: A large possible factor in why the direct-to-DVD movies and TV show never got very popular: the characters look downright horrifying in CGI.