Hard Core Players: if it rains, players who work with it and bash on no matter what. Players who get into the role and spirit of the game outline, and don't just show up in the same old gear they use at every event - put thought and effort into what the Admins have outlined.
Admins who can adjust on the fly to account for whatever happens and keep the game in motion.
Twists in the plot: those unique elements that throw everyone off for a moment to readjust and re-evaluate their tactics.
No BS: that includes players who play hard and call hits, as well as Admins who step in when required to minimize "discussions" if required.
Location/Set-up: even an older/used field can be set up in such a way that creates a new scenario and new challenges - new fields are not always the answer.
Momentum: no breaks, lunches, halts in the game....
One of the best games I remember was a WWII game where the one team had only loaves of bread, hunk of cheese and some meat in a pouch - realism added to the flavour of the game too!