it's hyperviolent but it's cartoon violence, and you can turn off the blood effects to tone it down a bit, right? if he's already seen a lot of that in realistic live action movies, i'm not sure it's something to worry about too much, especially if it's something the two of you are playing together so it's supervised and you can maintain a read on his reactions to it all and talk through anything as needed. maybe don't let him play it on his own for a few more years, but how many kids his age in the 90s played doom, quake, or counterstrike?
for more age-appropriate content it looks like people are recommending it takes two, minecraft: dungeons, any of the lego games, and splatoon but i've never played any of those.