If you've seen all of the Android Saga in Dragon Ball Z then you should know who and what Trunks is but I'll give you a short run down of his character below for those that haven't in the future *hits drums and symbols* reference and a general review that will follow after as well. (spoilers ahead)
Trunks is the son of Vegeta and Bulma or the prince (son?) of all Sayains. He first met the Z-Warriors during when Frieza came to Earth. Frieza came to Earth to get kill Goku and wanted revenge for his humiliation on the planet Namek. Trunks appears before Frieza. Frieza says buzz off, Trunks says a one liner then pulls out his sword while cuts Frieza in half like a hot knife through a stick of butter. Goku arrives shortly after and Trunks tells who he is and what happened in his future of how all of the Z fighters die to two androids built by Dr.Gero, this story takes place after the events of the movie but I wanted to explain what comes after and is worth a watch in itself but shows the character of Future Trunks through and through.
Future Trunks is a great character in DBZ and to my knowleage is the only character to have his own movie without Goku involved at all (besides the second Broly movie with Gohan and present Trunks). The story is based on the beginning of the android saga to the future where all the Z fighters, besides Goku, have been killed by andriod 17 and 18 and shows what the world looks like with broken down buildings and the state of decay of the fall of civilisation where Capsule Corp used to be.
The animation of this movie is superb one of the best out of all DB movies. In the HD version it is amazing and can't be over stated as well. Sound of the movie is crisp and clean. Since there are very few characters in the movie the focus of course, is on Trunks but Future Gohan makes its first and last appearance within this movie.
The overall score of this movie is a 8/10 if you've gotten to know a bit of background knowleage of Trunks or it would be hard to follow. If you want to get into this movie and haven't seen any Dragon Ball Z look up Future Trunks fights Frieza and come back to this movie if your interested in such things.
Or click this link to save some time: Trunks vs Frieza
Also I noticed I was surprised to see no one has posted a review about this wonderful movie, thought it deserved some love.