The 49-year-old, who is also working with Marvel on Deadpool 2, will play supervillain Thanos in the studio’s latest ensemble romp.
“I love doing Avengers, it’s maybe the most fun I’ve ever had,” he told Entertainment Weekly.
“I just saw a little snippet of it, and it was amazing. The cutting-edge technology of what they’re doing — what I’ve seen is absolutely mind-blowing.
“When I saw it on screen, it was me, but also not like me. It’s really strange.”
No official teasers or trailers have been unveiled, although some footage was released at D23 last month.
Still, those who weren’t there shouldn’t feel like they’ve missed out too much – as Brolin reaffirmed that the difference between that footage and the finished product is “not even close”.
A load of characters from the MCU are due to appear in Infinity War, but earlier this month Emily VanCamp poured cold water over the notion that Sharon Carter will be among them.
“With Marvel, they can give you a call the day before you shoot,” she reasoned when asked if she could still get the call.
“You don’t know what’s going on with their movies because they’re very secretive.”
Initial filming wrapped last month, but reshoots are still thought to be pending.
Avengers: Infinity War is out on April 27, 2018 in the UK.