The big problem is that there is a limit to what you can build (I hit it REALLY fast) so you can't really build a good sized community. Mine seem to hit 17/18 and that is the max. And has others have said, some can't be moved.
To be honest I am getting sick of the settlements because they keep calling me back with the same problem over and over no matter how much defences I put around the place.... and why the frack do I have to report back to Preston EVERY DARNED TIME THAT I COMPLETE A MISSION WHEN I AM THE SODDIN GENERAL... It seems an unnecessary step to complete each mission in my mind and every time I report in he has another settlement that can't do squat again... I had this one mission three times on the trot from the Abernathy Farm.. I was soooooooooooo close to just going over there and putting them out of their misery because they couldn't defend themselves from THREE RAIDERS EVEN WHEN THEIR FARM IS SURROUNDED WITH HEAVY TURRETS... grrrr.
Yeah... I was really looking forward to the settlement system but it just is the same missions on repeat, repeat, repeat. And then when I am trying to do the story I keep getting messages that I have failed missions... Being a General you should be able to delagate people to defend sites but it doesn't seem to stop the settlements getting people kidnapped or raided or respawning enemies in places you cleared out five minutes ago.
Yup... good game but the settlement system svcks.