As someone who recently changed to their third FC...
I agree with the other posts - fun and pleasant, no-drama.
Some things that were important to me:
* I got a personal invite ( and I was in the middle of nowhere). Didn't join based on a shout out.
* FC has a house and workshop.
* The members have purchased and decorated rooms in the house.
* FC members hang out at the house as a gathering point.
* We help each other. It's nice to be able to gather 8 people for maps, raid, etc.
* people are on-line when i am. You can get "good" advice.
* secondary issues: discord, FC buffs.

That said there is a personal aspect here as to what YOUR goals are. FC can have a Raid focus or crafting focus or ...