40k has been great for the social interactions, we transitioned from mostly boardgaming with some Necromunda (the gateway drug) into a ~10 strong weekly crafting/playing group. It's a good reason to get out with friends and praise each other's work. The sense of accomplishment from crafting is incredible and trading bits and tips keeps it fun.
For me, a big part of it is the looseness of the rules and the endless permutations of armies and possibilities. Getting schooled badly when someone works out a new uber-list is an excuse to figure out the new uber-list yourself. It's a sport where nobody gets to be the best for long (cross my fingers the CSM keep their 10-0-0 streak going).
Hell, it's better than football.