Started playing this game recently and I love it! Some features that I think would make it even better are:

-Raiders can drop armor and weapons

Whenever I first saw raiders I thought "awesome! Now I can get more weapons!" But then they didn't drop anything I think this is a reasonable feature as its not like their armor and weapons get up and run away in fear after the raiders die. Could make it to where raiders drop the weapons you see they have, or if a Dweller kills them, the Dweller's luck influences how good of a weapon the raider drops.

-Wasteland explorers can bring back Dwellers

When I look through my Dweller's adventures in the Wasteland, I often see them meeting people such as slaves, or injured sheriffs, etc. It'd be pretty awesome if some of these guys came back with your Dweller. I mean if I was a runaway slave, and this guy from a protected community that was looking for more people came along, i'd want to join! Could implement that maybe the Dweller's Charisma determines if the people they meet would like to join. But you also don't want more dweller's showing up then you can handle, so maybe make it to where only 1 or 2 people return with your dweller, like followers in the fallout games! And the people they could meet would influence the stats, for example if you meet a sheriff who would come back with you, the sheriff's largest SPECIAL would be perception, and could maybe come with a bad pistol. A runaway slave's best special would be agility, and so on.

-Dwellers explore the wasteland in groups

If your sending out multiple Dwellers to explore the wasteland at the same time, why would they NOT travel together? One possible thing to add to this would be a maximum group size. How the groups would work is any sized group would only find loot equal to what only 1 dweller would find, but would last longer. For example, if you send a group of 3 dwellers out, they would find weapons and armor equal to that of just 1 dweller, but they would last 3 times longer out in the wasteland.