You get far less money per kill in this mode, and the health of the zeds is ramped up to the extreme. Specialty zeds spawn far more often and in higher numbers here. You need to know what works and what doesn't here, or else you can screw over your entire team. For an unexperienced player, it's insanely unforgiving. Hell on Earth (HoE): The hardest difficulty in the vanilla game. Learning to hit headshots becomes important here.
Less money per kill, and zeds are far more resistant to your attacks. In suicidal matches, specialty zeds will spawn more often. This mode is recommended only for perk levels 15+, because you unlock your 3rd configuration at that point, something I will get into later.
Suicidal (SUI): This is where the difficulty starts ramping up. Still a little more money on kill, and the HP of every zed has gone up a bit Some special zeds will start *rarely* spawning here, such as the Gorefiend, the Elite Crawler, and the Alpha Clot, each bringing some mildly frustrating extra perk with them. Less zeds, more money per kill, and less health Learn the basics here and stick around this level until you've gotten most things figured out. Your goal is to survive the designated amount of waves and defeat one of (currently) 4, randomly selected bosses. There are various difficulties and lengths. This is your main gamemode, and the one that you'll spend the most time in (unless you're weird).