Black Cat was my first anime, and therefore I'm probably a little biased towards it, but I'll do my best.

The series centers around a former assassin, Train Heartnet, aka XIII of Chronos. After meeting a strange sweeper (bounty hunter) named Saya, Train eventually adapts a new way of life and thinking and parts from his killing ways. Along the way he meets Sven, a true gentleman who's actually in his late 20's despite his looks, and Eve, a young girl who's actually a nanotech experiment. The three become a team and go off on their merry way and catch bounties, not that they end up with much money after Train eats.

The art gets a little creative and weird with colors and angles sometimes, which makes you wonder if your screen is broken. Thankfully, those scenes generally don't last too long.

As far as bad content is concerned, there's a little of everything, but not huge amounts of anything. I watched it with my 9-year-old brother, and I'd consider it PG-range.

Violence - There are many fights, and a little blood, nothing excessive. Guns, swords, suitcases, and scarves are among the weapons. One particularly sad death. Train sometimes has flashbacks from childhood when he first started to kill.

Nudity/Sexual Content - Rinslet isn't exactly modest in her clothing choice,and at one point she wears a dress with a slit down the middle going past her chest. Rapists are mentioned as bounty targets, and they make a couple innappropriate remarks. There is one cross-dressing incident (a man dressing up as bait for a bounty, not for other reasons), and a transvestite tackles him in the alley. Purely for comedic purposes, and it lasts just a few seconds. Creed is... obsessed with Train (both guys)and walks around with way too many roses, but he's more interested in Train's abilities than anything else. Train is also totally not interested.

Theological - There is a group of antagonists called "Taoists" who use the power of Tao and their "ki" to enhance special abilities. So-called "spirit water" causes the abilities to appear. It's not explored much.

Problematic Themes - Sven smokes. Minor swearing, d***, a**, and h***, one use of b****. Once in a while, there's a drunk person staggering around and commenting like an idiot.

The anime is pretty loosely based off the manga. In the anime Sven and Eve meet Train while he's still an assassin, whereas in the manga the story starts after Train becomes a sweeper and they're all together. Personally, I like seeing Train all dark and assassiny with Saya and watching him change.

Sub/Dub - I fully watched the dubbed and parts of the sub, and they both seem fine to me. Jason Liebriecht (Train) has an awesome voice. The only major preference I have is with Saya's song, which is a million times better in English, in my opinion.

Sadly, the ending is rushed, and it took away from the story. I'd say if you want to watch something semi-serious, but not too serious, and with a bit of humor and romance, it's definitely worth a try!