There are three types of people that will view this movie;
1) Someone who is a die-hard fan of Gintama
2) The occasional viewer of Gintama
3) Someone who has never seen Gintama before
Because of these three categories, it makes reviewing very difficult, so I'll say this right now; if you are in either catergories 1 or 3, watch this! If you are in category 2, watch at your own accord.
The reason for this is simple, Gintama: The Movie is, in all honesty, a movie adaptation of the popular Benizakura Arc in the normal show. This movie is, in essence, a couple of episodes put together in a movie format...no ending songs in between, no recaps, no advert breaks...it is a movie after all. And that's the first thing I will praise!
The Benizakura Arc is my second favourite arc, not just in Gintama, but in my entire anime history! The fact that we get to watch this without having the annoying recaps at the beginning of a brand new episode, makes it all worthwhile. (Also, my favourite ever anime arc is another Gintama arc, the Shinsengumi Rebellion Arc, which is the defentition of brilliance and perfection).
As you can probably tell by now, I fall under the 1st category, but even so, there is some new content for people who watch the movie, as there are a couple of brand new scenes...scenes which were never in the anime! This alone made me buy this movie. Thankfully, in these new scenes, my favourite characters, (the Shinsengumi) who weren't present in the anime arc, get their own little scenes, which are awesome! And anyone that has seen this movie will tell you that, the scene after the first batch of ending credits, is one of the best scenes in Gintama history!
The story (yes, I'll finally explain it) is about Odd Jobs Gin, a mini company-for-hire consisting of members; Gintoki SAKATA, Kagura and Shinpachi SHIMURA. Gintoki is asked in a job to find a legendary sword, the Benizakura, whilst Kagura and Shinpachi are asked by Elizabeth (a weird alien-duck-man-directoroftheshow thing) to find their mutual friend Kotarou KATSURA, as he seems to have mysteriously dissappeared.
As you can expect, both their jobs end up leading back to the same place/person. An assassin from their past (a character that appeared a little while before the anime arc aired). This assassin is part of a group, lead by Gintoki and Katsura's old friend Shinsuke TAKASUGI (who is one of the best characters EVER!).
Another great thing about this movie, is it shows off everything that Gintama is known for; good story, emotional scenes, great fights and above all, the faboulous sense of humour! Let me tell you, the humour in Gintama is phenomenal, as anyone that is a fan of the show will say. Their ability to have an emotional scene and throw in some little reference to an anime, or make a joke about the way the movie is been directed, is very much the highlight of Gintama!
Overall, Gintama: The Movie is a movie I highly recommend watching if you fall into the first and third categories I mentioned at the beginning. If you are a die-hard fan, you will enjoy the new scenes and the joy of watching a great arc without any interruptions. If you are new to Gintama, this movie shows everything that Gintama is known for. If you don't enjoy this (not only do you have no soul, but) you won't enjoy the rest of Gintama as well.
If, however, you have seen this arc in the anime, but aren't a really big Gintama fan, then there isn't enough new content for me to recommend this. But, as I'll say again, you will have the pleasure of owning one of the best anime arcs for your viewing pleasure, at any time!
I, Mystotakun, take you, Gintama: The Movie, to be my favourite movie of all time! From this day forward, for better, for worse, for richer, for poorer, in sickness and in health, I will watch you, until death do us part!