If there is on thing that bothers me is that the rush percentage seems broken. I always try it when it's around 30% and the overwhelming majority of tries failed. On my last 10 tries I was only successful on 3, I counted. It seems like the percentage is inverted.
Still there is no reason to not try it since failing doesn't penalize you that much.
I don't understand how some people are having trouble making their vault dwellers happy. I have roach infestations and raiders attack all the time. Rushing resources generation usually fails and starts a fire, and my guys are like 96% happy. I really don't know what makes then happy or sad.
I think putting them on the job they do best makes them happy. Keeping all your resources at a minimal level helps, as does making babies.
I think the rush percentage is only one factor (perhaps this is decided partly on the worker's SPECIALs), and the other factor is the time remaining until you harvest your resource. Or you were just really unlucky.
My only complaints so far are the goals stop giving you lunchboxes pretty quickly. I've got nothing but caps for a while now. Not sure how I get more equipment without paying real money.
I keep sending my strongest guy out to the wilderness with the best armor and weapon I had, and on one trip he found a new outfit, on another he found new armor and a gun (separate events within the journey). I finally just got a new lunchbox goal with a harsh requirement that I keep someone wandering for 10 hours straight. So yeah, the pacing is slowing down a lot, even though rooms can be built immediately. Oh well, it'll be fun to toy with a bit more before it becomes a waiting room.