— On Saturday, Serena Williams goes after her 12th grand slam singles title in Australia against Justine Henin. It’s getting to that stage of Williams’ great career where you don’t want to miss it because we can’t be sure how many more there will be.

You don’t want to watch her just because she’s the best tennis player America has these days, but because she’s one of the best the nation has ever had, a notch below Chris Evert and naturalized citizen Martina Navratilova, but ahead of Billie Jean King, her own sister, Venus Williams, and everyone else.

It’s time to celebrate that greatness and the unique personal style she’s brought to the game, from cat suits to tennis boots to a white, warm-up trench coat. She hasn’t always been the most polite and gracious, but she’s never been dull. And when she’s on her game, few if any have ever combined speed and power as she has.

I’m not sure that American sports fans have ever fully appreciated Serena as much as we should. There’s always been outside issues going on with her and Venus, it seems. Most of them have had to do with their father, Richard Williams, who’s one of those guys who has a knack for ticking people off and a willingness to travel halfway around the world to do it.

But Serena also does a fair job of deflecting fame from herself with her own bad manners on court. She’s playing in Australia on probation for threatening a line judge at last year’s U.S. Open, and she’s had other moments that are not the sort you look forward to telling your grandchildren about.

Beyond that, her career has been cut in half. She exploded on the tour in 1999 when she won the U.S. Open at age 17. For the next four years, she was dominant. But in 2003, she underwent knee surgery. Though she won another Grand Slam two years later, she was ineffective for four years, dropping as low as 140th in the rankings in 2006. It wasn’t until 2007 that she fully regained her ability.

Had she not been injured — she also seemed to lose interest for a time as she concentrated on designing clothing and having a real life outside of tennis — her career would stand out more. Instead, it’s more like two mini-careers than one big one. And she probably would be pushing Evert and Navratilova for second-place on the all-time grand slam list.

She’s 28 now, which is bordering on senescence for a female athlete. Most women are washed up by her age, or at least ready to pack it in. But Serena seems as hungry as ever. If there’s been any erosion of her skills, it’s undetectable by any human sense.

This, too, is remarkable, but no matter how well she’s playing now, you know she can’t have many more good years in her. No one does in her sport at that age.

She’s not yet Brett Favre, ready to retire after the next big match. But she’s close enough to that stage where you have to start circling her grand slam finals and watching. You do because every one is history now. And each is one of a dwindling stockpile of championships she will ever play for.

She’s a force of nature, a once-in-a-generation player who does things differently than everyone else. No one’s ever quite combined raw power with unbelievable speed and quickness as she has.

I can’t think of another word for her. You watch her with your jaw on the floor, and when she’s really on, you wonder how she ever loses a game, let alone a match.

I remember Billie Jean, and I saw Evert, Navratilova and Graf at the height of their powers. I marveled at them all. Evert was the embodiment of silken elegance. Navratilova was relentless strength and aggression. Graf was graceful power personified.

And Serena?

Sheer awesomeness.