This Just Cause 3 [official site] video from IGN is titled "Just Cause 3's Challenge Mode Looks Insanely Fun." Insanely fun. You might like to watch the video because it has pretty explosions and scenery, but scroll down below the video and I'll explain why the challenge modes aren't insanely fun at all.
A lot of open world games are fun because of the things that are in that world: particular towns, or particular quests and dungeons. Often these are things that momentarily shrink the world down to a more constrained area or path. Just Cause is one of the few series though where the fun is more closely linked to its openness. It's a game not about missions, though those are there, but about the silly chaining together of action setpieces, from surfing atop a moving car, to tethering that car to a lamppost and swinging it off a cliff, to leaping from that falling car and wingsuiting down a mountain, to grappling yourself to the roof of another car, and so on.
Challenge maps don't allow for that, because by their nature they're about trapping you within a small box to do a single activity for a while. In the Batman Arkham games, say, that's great, because the swift kicking of endless goons is the whole pleasure of that game. In Just Cause, the freedom to fly across a tropical island is its joy, and that joy is nothing but diminished by a limited wingsuit track or a confined space to destroy.
There are people out there who love chasing high scores and I suspect extra modes will increase the perceived value of the game, but I did not lose my mind when I played these modes at Gamescom. They were mildly diverting and I'll never play them again.
Sure looks pretty though! For more on the better bits of Just Cause 3, read about Adam's time spent rampaging across its open world.
It’s a cartoon, a glorious slapstick world in which collapsing buildings somehow seem consequence-free, and Fast and Furious seems like the kind of thing that’d be written on the roadsigns. By the end of the day, I’d thrown myself out of so many vehicles that actually driving a car seemed boring. I put down my controller and reverted to looking on as other people put Rico through his paces. Somebody was making a grapple taut in an attempt to tear a bridge down through sheer force (didn’t work) and somebody else was trying to cross the island without touching the ground or taking control of a vehicle (did work)
Make your own challenges. Sounds like amazing fun.