The Haunted: Hells Reach currently has four different game modes to choose from: Inferno, Survival, Battle and Demonizer. There is no story or campaign mode available.
Every player comes standard equipped with a pistol, shotgun, SMG and a knife. Each weapon (except the special weapons) can be upgraded into a much more effective and powerful version. For example the regular shotgun turns into a Sawed-Off Shotgun, the SMG into a Commando Rifle; the Pistol into a Burst Pistol and so on. There is more information regarding specific weapons and their upgrades on the Weapons page.
Scattered around the levels, you can find special weapons which will take up a fourth weapon slot. These can be anything from a triple grenade launcher to an explosive bow. In addition to these weapons, you can find limited use explosives from Sticky Bombs to Impulse Mines. These can be thrown by pressing 'G'. If you have explosives in your inventory already, you cannot pick up more until you have used them all.
You also have several melee combat moves which allow to you either kill the minion or push them back to line them up for a shot. You can melee the minion with the 'E' key which will knock them back or stun them. Stunned minions have a yellow outline and if you go up to them, you can press 'F' to perform an execution move or you can simply shoot them or knife them. However, do not simply kick them while in stunned state as this could trigger their rage mode. Rage mode is indicated by a red outline. Minions cannot be stunned in rage mode, take increased damage and ammo to kill as well as their attacks being much more dangerous. Sometimes minions can trigger this at will though, so be careful.
At certain intervals throughout the game, a Chronostone will appear in random spots on the map. Your team must break this stone before the timer runs out (as indicated in the top right corner of your screen) or a level-specific natural disaster will occur which make the encounters very dangerous for a couple minutes at a time. Some of the types of disasters are Hurricanes, Meteor showers and Lightning Storms. Two other types of stones that can appear are Healthstones (a full heal if destroyed) and Soulstones (resurrect a dead teammate when destroyed). All of these stones can be stolen by minions.
There are currently eight maps to choose from: Night Frontier, Forsaken Canyon, Museum, Stronghold, Steel Town, Abandoned Mine, Lost Temple and Excavation.
Inferno
Inferno mode is a mode in which the objective is to kill all the minions until the end of the encounter. There are 4 encounters maximum and each one is more lengthy and challenging than the previous one. When you have completed all four encounters (the red bar is completely empty in the top right corner of your screen), you will spawn in what seems to be Hell and face the big boss, Abaddon.
Also note that in this mode by killing a minion with a melee attack or execution move will give you a small amount of health back, which is ideal if survival is top priority (*this is currently being tweaked by the dev team and will be fixed in later patches -- currently both melee and gun kills regen HP).
Survival
This mode works like any other Survival mode found in other games. Fight an endless wave of minions and try to live as long as possible.
Battle
Battle mode bears a resemblance to the Versus mode in Left 4 Dead. In this game mode, a total of 8 players (4 vs. 4) are split into the Humans and Minions team. The Human side play as regular while players on the Minions side play as demons that have a top-down perspective of the action, and can summon in AI-controlled minions by clicking the appropriate icon at the bottom bar. Higher level minions take longer to respawn and players can actually possess a summoned minion to harass human players. Player controlled minions are highlighted in a blue aura to differentiate themselves and players can even steal Stones and run around the map, having human characters trying to chase them down.
It is recommended that if you host a Battle game, that your PC and Internet connection are good enough to handle the player load.
Demonizer
This game mode is similar to the regular Inferno mode except with a couple of big twists. There are no waves or bosses to defeat and when a player dies, he is switched over to the Minion side and must go after the rest of the players. Should a minion player be killed by a human, that player controlling the minion will be revived as a human and the process repeats. The goal of this mode is to be the last man standing.