Pandaemonium in short
Pandaemonium is a third person Total Conversion of Half-Life 2 that will have the player guide their character, the Vampiric Mercenary Morthor, through several levels, such as urban sprawls, filled with various humanoid and monstrous enemies to engage in combat. During this, gunplay, tactics and acrobatics will all play an important role.
Gunplay will be important, as the best way for the player to 'win', is with superior firepower: avoiding their own death and thus a "Game Over" and killing the enemy first. Basically, their reflexes will be put to the test. Furthermore, certain ammunitions or guns will have an advantage in certain situations; the players will have to figure this out for themselves as this is part of the game.
Also, more often than not, Morthor will be outnumbered and will have to survive by superior tactics. As an example, he’ll have to figure out the behaviour of several patrols, destroy them one by one and attack the main group of enemies after that, to avoid being literally shot to pieces. Or in another example, luring the enemy with some accurate long-range shots to Morthor’s location, after which to use a lethal, but inaccurate shotgun, could be a valid tactic.
Acrobatics will help with the previous two goals. For instance, Morthor’s ability to leap large distances will help him to gain a better position to snipe the enemy. And when going head-on with an enemy, Morthor’s ability to dodge the bullets in certain conditions will come in handy as well.
Pandaemonium in detail
More details about Pandaemonium, including the backstory, can be found in the "Design Document", available as an .pdf file:
pandaemonium_design_doc.pdf, ~615 Kb