This is the exception every gamer should make for shooters.
Even if you 'despise' the shooter-genre as a whole, just give it a whirl.

Although the game is notorious for it's launch-time, when not run from an SSD. Once you get to playing, stopping after 'just one more game' will be your biggest challenge. And that says something, considering this ain't no easy game by a long shot.

ZED's are insane! Increasing the difficulty won't simply up their health bars. Nooo, these genetic miss-fits show up with: new enemy types, different movement patterns, extra abilities (which, usually, are a very visible representation of: "DIE M*TH*RF*CK*R DIE M*TH*RF*CK*R DIIEEE!"). Did I mention every higher difficulty supplies ZEDs with copious amounts of adderall (with just a pinch o' cocaine, and a lingering hint of meth)? These f*ck*rs are FAST! This game doesn't do 'hand-holding', neither does the player-base.

So don't go playing on difficulties beyond your skill-level, OK? You will die on numerous occasions ♥♥♥♥♥♥♥ around on HARD and SUICIDAL alone. Hell On Earth (HoE) however... well, it's pretty damn self-explanatory.
Although the game gives you complete control over 'how' you'd like to play, that being perk-wise (classes), or which weapons you choose to pick/upgrade, and where you hold out. There really only ever are 2 options:
Survive together, or Die alone somewhere at the other side of the map where you wont find your weapon again after you respawn the next wave.

If you can look past the down-right ♥♥♥♥♥♥♥♥-retarded micro-transactions (luckily they are more than optional, they're near next to useless anyway) and just recycle every crate or USB you get, and just focus on the Vault-crates you get from ingame accomplishments, you'll find a game with core-mechanics outranking any other Zombie-Shooter out there, and fun cosmetics to spice up you're ZED-shredder-extraodinaire.

Sidenote: I have rarely seen a game with options this decent; aside from graphics, keybinds and all that good stuff you'd expect from a AAA-title (which they never quite get right anyway). TripWire went so far as to even give you the option to turn Vocals on or off regarding the sick-ass Metal songs which keep you pumped during gameplay.

Endnote: If you respect your game-collection (which I'm sure is, 'vast as F*ck Boi');
BUY THIS, YOU NEED THIS BUT DON'T KNOW IT YET. There are only 4 games in existence as satisfying as this one. And none of them include slow-motion-zombie-slaughter-fests, so yea, like I said: BUY THIS!