Well zero is the first game in the storyline canonically, so not that hard to follow story wise. It's why it's called zero. You could play ace combat 5 first before zero, and stuff will make more sense that way as zero is a prequel released after 5, but doing so will spoil part of the ending of zero.
So it's a trade off you make, if you want to understand everything clearly and play in release order, 5 then zero, if you want the plot to unfold in canonical order and get surprised by all the plot twists, zero then 5.
It's what regular military history would be if fictional European nations were regularly building over the top doomsday weapons which need to be destroyed in a Star Wars trench run before they turn the rest of the globe into rubble. Ace Combat 4 had the Stonehenge, an array of giant fuckoff cannons meant to shoot dino-killer meteors off course, and it wasn't even the largest weapon in that game.
Ace combat zero has a pretty wild last third and ending, especially in conjunction with the lore of the strangereal universe.
how easy is it to follow if I'm vaguely aware of the concept of "the strangereal universe" but know absolutely nothing else
Well zero is the first game in the storyline canonically, so not that hard to follow story wise. It's why it's called zero. You could play ace combat 5 first before zero, and stuff will make more sense that way as zero is a prequel released after 5, but doing so will spoil part of the ending of zero.
So it's a trade off you make, if you want to understand everything clearly and play in release order, 5 then zero, if you want the plot to unfold in canonical order and get surprised by all the plot twists, zero then 5.
It's what regular military history would be if fictional European nations were regularly building over the top doomsday weapons which need to be destroyed in a Star Wars trench run before they turn the rest of the globe into rubble. Ace Combat 4 had the Stonehenge, an array of giant fuckoff cannons meant to shoot dino-killer meteors off course, and it wasn't even the largest weapon in that game.