Heretic was the first to come out in 1994 and was built upon the game Doom, which was very popular at the time by the company Raven Software.The game takes place in a world where 3 brothers known as the Serpent riders (they ride serpents) have corrupted the world with their evil ways. Which basically means lots of imps and demons and skeletal beasts have to be disposed of by the player while navigating maze like levels, such as castles dungeons and the gates of hell, that are quite pretty considering it's age! It was apparently the first game to have "giblets" of gore and even carries a warning for this (though it is very tame for today!).

Hexen came out in 1995 as a semi sequel (it's an alternate dimention!) and is the German word for Witches or spell casting. It is noticably prettier than the other title (the levels with the stained glass are nice, though it looks less great in a screenshot!). It also allowed you to have a choice between 3 characters with different weapons and styles of combat.
There was also a new set of enemies like the Ettin (look left), Stalkers (its basically the creature from the black lagoon) and the Wendigo.

Attacked by a viscous spider!
Hexen 2 was the last official Hexen game, and was the first of the series to be completely 3d (in earlier games the enemies and objects are just pictures!). It also added things like upgrades for character and 4 new player types (Paladin, crusader, Necromancer and Assassin) as well as sheep.
There is also new enemies like the skull wizards, gorgons and spiders. So if you are arachnophobic this one might be a bad idea...

Heretic 2 from 1998 I don't have, so no screenshot! This was the first in series to be third person (where you can see your character instead of seeing the world from their eyes) and was also the last in the series. It's more cinematic than the other games with movie like sequences to narrate the story.

Fear the mighty skull lamp!!!
Hexen: Edge of Chaos is an unofficial sequel of Hexen, built on a much more modern game (doom 3) began in 2010 by a group of fans.
It features the characters from the original Hexen along with the same enemies, and weapons. the best part about it is the lighting, and the way that your lantern and weapons cast long spooky shadows!
Hopefully they finish it soon, and the best part about it is that it should be free! (there's a demo version availible, though you will need to own Doom 3).

This post is part of the A-Z Blogging Challenge, 2013.

More screenshots after the cut!