I'm actually reading this series to my (almost) 12 year old daughter right now, we are almost through the first series (including the Superman crossover).  She likes it a lot.  There was one uncomfortable scene in issue 2 where Carnelian tries to force himself on a captured Amethyst (icky especially given she starts on Earth at age 13), but other than that it has been fine.  I hadn't read this since it first came out.

I do think it would definitely suffer with the lack of color.  There is a strong emphasis on it, with the 12 different Houses based on colored gems.