Tekken gets so much hype because it is by far the greatest fighting series ever made. There are many reasons it is the best, such as the wide diversity of characters and fighting styles, but first and foremost is the superior control system. It is just far more logical and intuitive than the competition. It honestly astounds me that other fighting games have not adapted to have one button for each limb like Tekken does, it just makes so much more sense. And most of them still have a block button, which Tekken has rendered obsolete.
There hasn't really been much evolution of single-player fighting games since the days of Final Fight, but as far as multiplayer goes, Tekken reigns supreme. There is simply no better 2-player game in existence.
I expect Tekken 6 to be the greatest fighting game ever made (unless they pull a Tekken 4) but I also don't expect it to have advanced much beyond Tekken 5 in anything other than graphics.
If they finally pull off a decent story mode it would be awesome, but I am not going to get my hopes up.