There are so many opportunities to spoil this film for future viewers. So much 'stuff' happens, stuff that's a big deal, that will shock you.
But as we trooped into a packed IMAX screening theatre last night - we were amongst the first in the world to see Avengers: Infinity War - the screen warned us, with the face of supreme evil guy Thanos: "Do not spoil this film for others."
So what can I tell you? Well I'm going to avoid detail but after 18 movies worth of saving the world, Marvel's superheroes assemble en-masse, to face their biggest challenge yet.
The film is over the top, exhilarating, so loud, ridiculous, with shades of The Lord of the Rings and hints of Harry Potter in its visuals, but threading through it all, as ever, is the hilarity.
Each moment of seriousness - and there are some dark moments - is followed by the trademark wisecracks courtesy of Thor and the team.
It really is a very funny film.
The audience whooped and clapped and gasped - there are some shock departures I can tell you - or rather I can't tell you. Very unexpected.
I've seldom seen such a line up of A-listers. The Russo brothers, directing again, must have had a field day getting them together - or pretending they are together at any rate.
It will break the box office I suspect and there's another one to go, in the world's most lucrative film franchise.
I confess I'm not a Marvel superfan. I've seen many of the preceding films, but not all. But you can't help but we swept along with the sheer energy and invention of the film. I can't wait until the next one.