Ps4 so weak can't handle ?
There is never going to be enough graphical power to handle everything. To produce CGI movie level of graphics, 5 minutes of video may take 24 hrs for a super computer to render. In a video game, the dev has to pick and choose, what to focus on, what to sacrifice and leave behind to achieve a good compromise of real time performance (as well as production budget, production schedule).
If a dev makes a single scene with lots of bells and whistles (and puddles and reflections), it may perform well, and they may capture a trailer video from that. But when they put the whole game together, they may find that the scene is going to take up too much memory, for example, cos it's an open world and they have to load other scenes into memory too, or the CPU has to compute other things outside of the current scene. So they may be forced to downgrade the current scene.
I have no issue with such downgrade, especially when the trailer was early footage, when it's clear the dev wasn't intentionally trying to false advertise. So long as the resulting quality isn't too far off, I am ok with it. The focus should be in the gameplay itself.
My worry is more about the open world becoming empty or nothing to do; or at the opposite end, too many things to do but very repetitive. This is subjective, like FF15, many people (especially westerners) loved it, while many people (especially Asians) hated it. Some people complain that the collectibles are these backpacks stuck to walls with spider webs... there is just no possible logical explanation for them. Personally I don't mind that at all (Riddler leaving little puzzles all over Arkham isn't any more logical anyway).
My reservation is that I don't like Arkham style of reactive combat (wait for enemy to attack, bat sense goes off, QTE the parry for big damage), so I am still on the fence with this game (though Spider-Man's combat is a bit different from Batman), but that's just me, most people like Arkham style.