After discovering Yakuza with 0 shortly after its release, I've since played Kiwami, 3, 4, and now halfway through 5. I have 6 in a blister and will play Kiwami 2 once I'm done with it (didn't want to ruin 6 by playing the more recent one first). Every time I finish a game I decide to take a break from the series so I don't get burned out, but soon I feel like going back to this world and its characters.
So far, 0 is the best, and I think 5 is second. I like how rich it feels without it feeling like filler content, there are several cities and playable character, each with their own big minigame. Also, I liked 4 but thought that Saejima really dragged it down, but in 5 his section is much more enjoyable, at first I was bummed that he was one of the playable characters (would have preferred Tanimura) but in the end I had fun with him and his minigame with was a welcome change of pace and scenery.
Ooooouh yeah! It's my most anticipated game along with Rebel Galaxy Outlaw. I hope we get to play around with the combat system a bit more, and try out both styles more than just for a few seconds against a weak opponent. From the first demo, I really couldn't tell the difference between the two styles, they are both fast, acrobatic, and using both fists and kicks. Also I'm pretty sure the grabbing attacks were the same for both.