Info about HeroQuest 

What makes HeroQuest unique? One player assumes the role of Zargon/Morcar the
evil sorcerer and controller of the game; the other players assume the roles
of the heroes -- the Barbarian, the Dwarf, the Elf and the Wizard. -- A game
for 2 to 5 players, HeroQuest is played in 14 sequential game playing
sessions called quests. Each quest is described in detail in the quest book.
-- One quest may take an hour or two to play, with each subsequent quest
increasing in difficulty. -- during a quest, a hero may acquire valuable
treasures. These riches may be used between quests to purchase powerful
weapons and protective armor from the armory. -- The heroes work TOGETHER to
defeat Zargon/Morcar and his forces of chaos. Individual winning is not the goal.
United the heroes stand. Divided they fall. -- The adventure never ends...
Additional quests, featuring all new challenges for the heroes are
available in quest packs (sold separately.)

ADD-ONS  FOR HEROQUEST

There were two Quest Packs released in both the US/Europe/Australia/NZ&UK
Kellar's Keep
Return of the Witch Lord

Two Quest Packs were released only in the US: 
Elf Quest Pack (with the quest booklet "The Mage of the Mirrors")
Barbarian Quest Pack (with the quest booklet "The Frozen Horror")

This Quest Pack was released only in Europe/Australia/NZ&UK
Against the Ogre Horde

These two Quest Packs released in Europe/UK only

Wizards of Morcar
HeroQuest Advanced Edition contained the quest The Dark Company

Released in Europe/UK only

Dungeon Design kit

In addition the Adventure Design Kit was released in Europe. This is not an actual Quest Pack, but a kit to use in designing your own quests.

What order should the quests be played in? 
The quest packs themselves contain hints as to the order of some of the quests should be played in. After the basic quest book, there is a page detailing how
the Emperor was trapped in Karak Varn (Kellar's Keep). In Against the Ogre Horde, Morcar (Zargon) laments his failures in Kellar's Keep and with his ally
the Witch Lord. In the same quest pack he sends out his Chaos Warlock Festral, who returns home in Wizard's of Morcar in failure. Using these clues these
quest packs should be played in this order:
1) Basic Game Quests
2) Kellar's Keep
3) Return of the Witch Lord
4) Against the Ogre Horde
5) Wizard's of Morcar
There are no other clues as to where The Frozen Horror, Mage of the Mirrors, or Back Company fit into the list. I would suggest playing them after the first 5
quests. Any other ideas? 

Three HeroQuest books were released in the UK. Two of these contained single level, solo quests: 
The Tyrant's Tomb by Dave Morris, contained the quest A Growl Of Thunder, a solo quest for the Barbarian.
The Screaming Spectre by Dave Morris, contained the quest Running the Gauntlet, a solo quest for the Wizard.