The time-travelling war movie is among my favourite film sub-genres, almost perfectly expressed in the 2014 Tom Cruise film Edge of Tomorrow, a cheeky blend of comedy and effects, with Cruise and Emily Blunt's military recruits repeating a single day thousands of times until they work out how to kill an alien invader.

Most lucrative of the genre, and forgetting its woeful 2015 outing for a minute, is the Terminator series, where a succession of robot assassins are sent back in time to kill the future leader of the resistance to an electronic foe.

Chris Pratt, star of The Tomorrow War, is the son-in-law of Terminator star Arnold Schwarzenegger, and looks set to enjoy carrying on the family mantle of action hero icon.

Not all of Big Arnie's films were winners and I think The Tomorrow War isn't going to sit among the best of the Chris Pratt oeuvre.

But the new Amazon Prime release, now streaming, doesn't deserve the overly harsh critiques it is receiving online.

This big-budget feature doesn't hold back on what the genre wants - an alien foe well executed by its CGI team, a clipping plot and lots of explosions - all things its audience will love.

In the year 2022, the world receives another global seismic disruption when military forces from the future - the year 2051 - arrive to tell of an unstoppable alien invasion that has brought the world population down into the hundred-thousands.

The future military conscript soldiers from the present-day to jump forward and help with the planetary defence.

Among the conscriptees is Dan Forester (Pratt). In 2022 he is a high school biology teacher, frustrated that his career doesn't use him to his full potential as bench-scientist and researcher, but his life is full with loving wife Emmy (Betty Gilpin) and whip-smart daughter Muri (Ryan Kiera Armstrong).

Emmy is a counsellor for the handful of veterans that return from the future war, with their missing limbs and their damaged psyches, and so she knows what Dan is facing in the future.

With the planet desperate, Dan's fellow conscriptees are a rag-tag group who have no place picking up a weapon, including the nervous over-talking businessman Charlie (Sam Richardson).

I'd like to see the bullet count once the travellers arrive in future war-torn Miami. It seemed like the firing went on forever, which feels fitting for a movie about time.

Meeting the conscripts in the future is Colonel Forester (Yvonne Strahovski) who has a mission for Dan as possibly the only hope for saving the human population.

There is one big thing lacking in The Tomorrow War that holds it back from its full potential, and that is humour. Comic timing is what turned Pratt from TV actor to action star in the Guardians of the Galaxy and Jurassic Park films.

The film is nearly two hours through before the first signs of comedic life emerge, as Dan, Charlie and J.K. Simmons' veteran father to Dan take a world road trip. This last quarter of this long film is rollicking and cheeky and had it been like this throughout, the film would have been much better for it.

This film would have looked brilliant, its sound design immersive, had it come out in theatres as I'm sure the producers originally intended, but with the world still partially locked down, its audience on Amazon's streaming service is potentially much larger and certainly hungry for the loud distraction.

As far as the performances go, Pratt serves his role better than it serves him, and Simmons is terrific as usual. Betty Gilpin, whom viewers might recognise from the Netflix series GLOW about a womens' wrestling team, enjoys a fine supporting-wife role, though again she deserves better. If you want to see her in a role that uses her properly, look for The Hunt on iTunes. I feel like the winner out of this film is going to be Sam Richardson who nails the comedy sidekick role and gets the bulk of the film's handful of laughs.

Note that as The Tomorrow War isn't out in theatres, it didn't need to apply for a formal classification rating, and so that M is my own estimation, based on its violence and bullet count.