Simply put, almost everything is wrong in this game. Gameplay is like a reskin of fortnite's gunplay and traversal minus the building part. None of the playable characters have unique/interesting feat specific to themselves.
We've got Deadshot with a simple boring sniper without any bullet reflection ability(like the feat of hitting a target indirectly using walls or other obstacles or even hitting multiple targets with just one bullet) also seen both in suicide squad movie and arkham games. He's just like another marksman in call of duty with a jetpack(which isn't even a part of his original arsenal)
Harley quinn plays just the same only that she's got pistols and swings around using grapple gun on a drone. No joker bombs or even jack in the box she used to have in arkham knight dlc. Another character with pistols.
Captain boomerang... Or just captain. Doesn't even use boomerangs. His traversal(which isn't even his, he stole the flash's speed force gauntlet and now magically can move fast for a short distance. Another character that uses guns instead of what he's supposed to...boomerangs.
King shark uses guns too. But guess what... He can't even swim!
There're no different mission modes in the game other than dodge and gun. No stealth, no Just Cause like explosions, no nothing. Just some 'go and fetch this' kinda things in long boring walks.
Justice League is only consisted of the flash, green lantern, superman, batman, wonder woman(which we don't even get to fight her) but no matter, they're all easily beatable and are near nowhere challenging as they're supposed to be. Their deaths aren't satisfying either.
Also, there are no aquaman, zattana, martian manhunter, shazam etc. No bat family from Arkham games like they all just vanished! Teen titans don't seemingly exist.
Suicide squad is incomplete too. No deathstroke, reverseflash, killer frost, manbat etc.
Graphics and lighting might be the only positive thing in the game (while still, lois lane and WW look much worse than their comic versions)
Story doesn't make sense since all of the league members are nerfed to feed the squad's plot armor. Near to no consistency with previously told arkham story(yeah, they tried SO HARD to explain everything in the arkham museum part but it just doesn't show in the game)
Buy only if you don't give a f# about any of the characters/dc universe and are just looking for another shooter game.