I tend to really like Rimmel cosmetics, unfortunately, Rimmel Extreme Definition Ultimate Lash-Separating Mascara was not all that ultimate for me. Not at all.
This mascara has a pretty strange brush. It looks like a little plastic comb, and I found it very difficult to use.
First, it difficult to wipe the excess off. Second, it is a bit hard to get it pointed at the correct angle. The result for me was a big smear by one eye, and a bunch of clumps on the other. I was quite unimpressed.
Rimmel is featuring this style of brush on their fairly new Lash Maxxx mascara as well. It really just didn't work for me.