Just a thought I had from a chat conversation.
When The Enclave appeared in Fallout 2, they presented a huge sock factor. When I first saw Frankie and his escorts I was like "Shit, the Brotherhood have changed".
I mean... Who else had power armor, right? That there was a US government remained a mystery until much later in the game... (I guess it kinda helped maintain the mystery that my early playthroughs went to New Reno before Gecko - I got the NR vertibird before the Radio Comms guy).
When eventually it was revealed they were the US Government, it was a huge shock. I mean, The USA are the bad guys? This can't be right... I wouldn't say its unprecedented, but it is so out of the ordinary - especially for a game made in California, not Tehran.
So for me, the biggest mistake that the Enclave were ever involved in is... Being used twice.
Yes, being able to walk around The Mall to Enclave Radio is epic, I can't dispute that - its one of those lovely ironies that makes Fallout, Fallout.
But once the shock factor is gone, its gone. You cannot put that genie back in the bottle; it also didn't help that Fallout 3 gave up the jig early on - for even a new player there was absolutely no secret in who the Enclave were at the end of the day, and that they were the bad guys.
Yes the Enclave are popular, but so are Doctor Who's Daleks - we can go years, decades even without seeing our favourite Nazi-Pepper-Pots, and even then they face accusations of going overused and cliche.
The mystery and intrigue with the Enclave are gone. They've been pretty much obliterated twice now. How do you make them sexy again?