My Vault is getting huge and I'm up to 66 Dwellers out of a possible 200 I can have.
Early on, I wasn't attached to any of my little Dwellers, but now I have favorites that I know by name. I'm highly protective of all of them, and grab new Dwellers who show up at the Vault door and quickly drag them in to safety.
There are some new creatures which can show up in your Vault that look like mutated gophers. They might be just a bit tougher than Rad Roaches.
An uglier upright form of these showed up at the Vault door one day. They blasted the fully enforced door down like it was paper, and blew past my two reliable door defenders (no Raiders ever get past them to the second or third room). Gleefully they went through each room and got as far as the third level !!!!! Before my Dwellers took them out. As many as four Dwellers died in the attack, something that hasn't happened in ages.
I'm glad I give armor and a weapon to each Dweller as soon as they arrive. No Dweller is without defense, but many haven't been trained in Strength and Endurance, if they're in rooms where Agility or Intelligence is important. I had just moved my "best" people up to the top rooms the day before the big raid. Good thing. I'm going to work to get everyone in tougher shape if the attackers are going to be tougher.
I sent three of my best Dwellers out yesterday morning and I usually will bring them back home before day's end. (sniff) I forgot about them till about midnight when I was settling in to sleep. Only one died, and another was close this morning. A good Overseer watches out for their Dwellers, tsk.