"A bunch of superheroes get together and save the Earth," is how Rachel explained the plot of Avengers Assemble to a colleague at work before we went to the movie.
And that pretty much sums it up. With little, or no, foreplay the audience is thrown into the action from the get-go (with the first couple of scenes already subtly setting up the sequel before we've even seen this first film).
Don't expect any pussy-footing around, it's pretty much taken that going-in you know who these characters are and have a rough idea of what they can do.
Loki (Tom Hiddleston) comes to Earth to seize control of the Tesseract (aka The Cosmic Cube) to open a gateway to the planet for his alien army (but where did he get the army from... or more crucially from whom?) and in the process pisses off Nick Fury (Samuel L Jackson) and SHIELD.
Fury sends out the Black Widow (Scarlett Johansson) to help him assemble a team of heroes: the Incredible Hulk (Mark Ruffalo), Captain America (Chris Evans), Iron Man (Robert Downey Jnr) and Hawkeye (Jeremy Renner) - who starts out mind-controlled by Loki.
From there Joss Whedon's basic plot unfolds as two major fight scenes (one on the SHIELD Helicarrier and one in New York) stitched together with some talky stuff. This isn't Marcel Proust, this is pure superhero testosterone and all the better for it. As long as you've enjoyed one - or more - of Marvel's other recent superhero movies (e.g. Captain America, Thor, Iron Man etc) then Avengers Assemble will take you to your happy place.
Every hero gets his moment to shine (particular stand-outs for me include the Hulk "negotiating" with Loki and Hawkeye shooting without looking, but everyone has their moment in the sun) and play to the strengths already shown in their earlier cinematic appearances.
There's all the banter and surprises you'd expect from a Joss Whedon script, an unexpected death and a post-credits sequence that sent tingles down my spine.
Basically, for comic book fans, you couldn't ask for anything more from a superhero team blockbuster.