Besides questionable story and how its presentation the main problem with the gameplay is consistency. A lot of things are inconsistent or even random: the damage NPC take from you, AI behavior, grenades radius... The last example, that prompted me to write this before I finish the story was the case of fall damage. In Caspiy I've jumped into dried out seabed near a derelict pier and... Died. Even though it was not that high. And just a few minutes later a demon caught me and dropped me from much higher and... I did not die. Even though I was dropped on my back. This does not make any sense to me.
Also, it's clear that the goal was to make a sort of Russian "Borderlands", but... To begin with, social aspect of Borderlands' setting was quite far from realistic (at least in the long term implied there), but it was intentionally humorous and exaggerated, so it worked ok there. Metro Exodus is going for a more realistic and "grounded" approach and thus Borderlands' formula does not work here.
And the thing is, the "grounded" approach did work well for the atmosphere in the previous games. It was not just linear maps. Somehow, despite playing with cheats (I prefer to get through most recent games as fast as I can), in previous games I wanted to go stealthy, because it felt natural. In Exodus, while I do try to sneak, I do not feel that motivated, because I do not feel as much "weight" in the fights (especially with this AI).
Of course I could waste some time and do something like what I did with Detroit or The Medium and make a whole list of what's wrong here, but it would be such a pain to do that, because of that many flaws, that could have been fixed to make both gameplay (yes, I am looking at you, "Hold X" prompts) and narrative.