They have not bothered with any English Voice Acting for this version. Any reason behind it? Is the series not selling well so they have had to cut stuff from the game?
I don't really know.
Koei did lose quite a lot of sales from the last few games as they were not as good as the others. The only other possible reason I can think of is that for a lot of the games previously, people have complained about poor English voice acting and how it hasn't been on par with the Japanese versions. I actually agree with this, the best English voice acting of a DW game was 3 and 4. After that it all went downhill. So I don't mind the dubs myself ^^.
Is this game worth getting?
Will they release a version with English voices?
All depends on how much you like Dynasty Warriors plus it's not a full price title anyway (at least not in my country). English voices won't be added. Think they are cutting down on costs so they got rid of the English Voice actors and i'm guessing it's why there's no Xbox 360 version.