"Zombie" is a name assumed for the sake of convenience rather than accuracy, because it is really a misnomer - the zombies of HotD are a step removed from the conventional image of ravenous, putrescent shamblers. While it is possible to reanimate human corpses with certain drug treatments, the vast majority of 'zombies' are actually artificially cloned biological weapons. Indeed, the DBR Corporation was originally licensed to research and manufacture zombies for military purposes - they were designed to be disposable fighters, cheaper and less controversial in that they prevented real soldiers dying on the battlefield. Zombies were given the outward appearance of decay to touch on mankind's primal fears and so increase their aura of horror and intimidation, and the images of entropy and oblivion also suited Dr. Curien's own nihilistic worldview.
Consequently, 'zombies' can have strength, stamina, and agility far in excess of the stereotype of wasted cadavers that you can outpace at a light stroll. They can sprint, wield weapons and heft and throw objects of weight without worrying about spindly bones snapping. There are also multiple types and classes of zombie, adopting forms widely divergent from the human norm, from bulging and sinewy hulking brutes to scampering gymnastic pygmies, mutant demon-like dogs and swollen, pulsing maggots.
Still, they haven't departed entirely from tradition - a shot to the head will put down one of Curien's children just as readily as it would an extra from Night of the Living Dead.
One small advantage of fighting a Curien zombie is that it has been specifically built as such, rather than warped from something else. There is no communicable body-mutating 'T-Virus' analogue in House of the Dead; being injured or bitten by a zombie will not result in the victim transforming into one.
While basic zombies have considerable physical abilities, they lack advanced intelligence and so still tend to resort to unimaginative living-wave attacks. "Hunting Packs" roam the landscape freely, seeking humans to kill - once one is discovered, packs will converge, mob up and swarm over the target, crushing it through weight of numbers.
Zombies are also apparently responsive to instructions from certain individuals and will follow their orders without hesitation. The process by which this is achieved is currently not known.
TYPE-22: The High Priestess
In Resurrection Men part one, the vast majority of zombies appear in Sophie Rogan's flashback. At the end of the strip, Agnes releases 3 zombies into the room where Sophie is being interrogated. Sophie incapacitates one with a pole, but another knocks her to the ground. The remaining zombies are put down thanks to the timely intervention of Thomas Rogan with a shotgun.
In part two, the zombies of London begin to converge upon Grosvenor House from the Tube, having been summoned by Agnes via the dragon line, and attack the AMS agents in the red bar. The zombies who haven't been taken down by G, Thomas and Sophie are quickly wiped out by Lisa with a molotov cocktail. As the story ends, Sophie ponders on NAOMI, which will destroy the undead horde and replace them with something far worse.