100,000 enemies on screen
https://www.pcgamesn.com/serious-sam-4-planet-badass/serious-sam-4-enemies
I was going to say the graphics look kinda weak but with 100k enemies that's understandable.
SS3 was okay but I don't quite know how you'd make it much better without changing the basic gameplay. Maybe more types of enemies, big boss battles, and some faster movement options. Or they could go for more environmental destruction / interaction.
If they change the formula people will piss and moan its not SS any more.
They are really in a hard spot I feel.