Style, not really. Tattoos tend to look a certain way for a reason and while I think there are some artists who can push the boundaries of what a tattoo looks like, I think it's important to recognize the constraints and limitations of skin, and part of that means that you can't do just anything with a tattoo and expect it to age well. I think the tendency as of late towards "watercolor" style tattoos is an example of that: I think that some people's tattoos in that style may be okay, I'm thinking in particular of Amanda Wachob's tattoos because they're abstract and don't rely on readability in the way that something figurative does, but a pastel-coloured bird with no black outline...forget it, that's nothing in five years.
As for subject matter, pretty much anything is game as long as it can be tattooed as a strong image.