Also you have to be able to grab and climb on everything, so they can't skimp on detail like the sides of buildings, and rooftops.
There was this great video I watched years ago on inFAMOUS 1, and they were displaying the calculations overlay that they had to program to make sure that Cole could actually climb on every surface he was supposed to climb on in the game. Hundreds of buildings, thousands of little handholds, poles, wires, windowsills, etc, etc. It was fascinating. And absurdly complex, and they were talking about all the bugs and glitches that kept happening when a calculation would misfire. I don't know if you've ever seen the bug in inFAMOUS 1 where Cole's arms will get super long, as he is attached to something very high above him, but his body is much, much lower. Looks like Mr. Fantastic. Lol.
Second Son is 50% larger than New Marais, and judging from these screenshots, it's also packed with tons more buildings. I think people are selling Sucker Punch and Second Son short, but you can't take away that the game was made by 80 people compared to Watch Dogs 500, and it's improved significantly over not only the previous entries in the series, but the early reveal of the title a year ago.
I've mentioned it a billion times before, but I saw the game live at E3 last year, demonstrated on a 55-60" HDTV by Sucker Punch devs, and it looked fucking incredible, but these compressed screens look even better in terms of the detail, AA, particles, etc (the only thing the screenshots lack is that super crisp sharpness that you'll see on your actual set, but the Share button always muddies).
80 people made this game. 80 people. Sucker Punch should be fucking proud.