Hi, Conquest player here. I know why every other LCG appeal to people:
StarWars is StarWars.
A Game of Thrones is a medieval setting about some noble houses fighting about the iron throne. It got books and most importantly the series now which show how cool it is.
Arkham Horror is about the supernatural and some people seem to like it (I don't see the charm in it but I'm mostly jaded since all the arkham horror boardgames are cooperative).
W40K Conquest is the Warhammer 40K universe where there is
only
war.
Gamemechanically, Conquest is awesome since it's quite deep and all factions have different playstyles.
Space Marines
are resilient and have powerful combattricks that deal more damage or prevent it.
Imperial Guard
are truly weak but numerous and always got more units than you though. Their warlords strenghten their weak units and got abilities that kinda sacrifices one of their weak units AND one of the enemies.
Eldar
are specialized, as strong as Space Marines(!) and focus on exhausting (tapping) their enemies and bringing their units back from the dead temporarily.
Dark Eldar
can't take damage but they deal it out aplenty! Their playstyle is to win the battle before it begins by discarding your cards, removing your units or killing them outright! If they have to fight, ranged units are there.
Orks
are strong and get better when they have taken a bit of damage. Their gameplan is to get damaged and hit back even harder.
Chaos Space Marines
have difficult to use units with difficult to use abilities and powerful daemons that can be made cheaper with your cultists
Tau focus on attachments that make their units stronger and they got a lot of'em! All their units are special in some way (ranged, stronger command, get back resources etc).
Legend of the Five Rings is a universe I have never heard about until here on Fantasy Flight a few months ago. So it's about some samurai clans that clash....is there magic, undead, Dark Elves and the like?
Was the mechanics of the L5R CCG as good as Conquest (the best I've ever seen!)
I guess it boils down to that all other LCGs have exciting universes while I've never heard of L5R and some samurai clans fighting sounds like: "ok...."