To finish off the casting round, we have the Murata siblings and the Shinsengumi.

Click for original size( The Murata siblings )
Click for original size( Cut for the long-awaited Shinsengumi trio )And that's a wrap!
I think it's a good mix of people who are reliable at acting, and a few unknowns cast in roles that won't require a huge amount of acting. Will that make it a success? Who knows. Japan has gone full steam with live adaptations of manga works in the past few years, and there's been a very small handful that's really struck gold with audiences (
Rurouni Kenshin being the only one I can think of).
Just in the next few months, from the ones I've heard of, there's going to be
Sangatsu no Lion,
Blade of the Immortal,
Full Metal Alchemist - not to mention at least another half a dozen romances coming to either the big or small screen. Generally Japan has better results with small screen adaptations of shoujo manga, but has traditionally struggled with shounen due to the scope, often the much darker themes, and the occasional leaps in suspension of belief required of the audience.
Possibly a good comparison will be the Oguri Shun-led
Nobunaga Concerto, another historical fiction that has its comical and serious moments. It managed a respectable result at the box office and became the first film to squeeze
Star Wars out of its top spot.
It will depend very much on the script and even at the best of times
Gintama is not an easy material to convert into live action. Even just converting from manga to anime, given some of the crazy premises and the dependence on comedy, is no mean feat and speaks volumes about the professionalism of the writers and actors, and the maturity of the animation industry in Japan.
I have some carefully measured hopes, but given some recent failures in translation of popular manga onto the silver screen, I'm also carefully preparing myself for a disappointment.