I'm going to laugh when it's just a psychological thing that just makes you think it's harder.
Its not, there's fatty's everywhere, the levels are more densely packed with gun toting goons, melee is practically not an option unless you're fucking hardcore, guns carry less ammo and every time you drop a gun it loses more ammo (basically take a shotgun with three rounds, you swap it out real quick for a machete, you come back after melee'ing everyone to find that the shotgun has one round), the levels are inverted, there are more visual effects to fuck you up (AKA: The higher the combo the darker, wobbly, and flashy the screen gets). And on the very last level if the rumors are true, the controls become inverted.
Basically: Git Gud 2 Ply Hard