What's your favorite little detail of Fallout (any Fallout)? Mine would be the slides during the loading screens of FO3. I loved how they looked,the information they provided, and I especially loved the sounds they made when switching between slides.

You can change the hud color, most games don't offer this without modding the files and I really apreciate it. I always change it to blue.

I love how we can actually see an arm rise into view with the Pip-boy on its wrist whenever we activate the Pip-boy. I wish they'd do something like that in TES (two hands holding a map in front of you face when you hit the map key, holding an open bag when we hit the inventory key, ect).

I really like the modern day pop culture references in fallout 2, even just minor things. My favourite being the blues brothers line when you first recruit Myron.

I like in fallout new Vegas that every town and settlement has some sort of economy and reason why it's there. Many people dont notice these small things. Where in contrast, fallout 3 has lots of settlements that have you scratch your head. Why do people live in a town with a nuclear bomb and irradiated water pool in the center? Why is the biggest settlement on a sinking ship in irradiated water, surrounded by hostile territory. How do the caravans not get slaughtered?

I loved in fallout 1 where you could type in questions to ask npcs, and they will give answers that werent covered by the questions you could normally ask. It extended my conversation with the mutant lieutenant for example.

I loved in fallout 1 and 2 how there was a target for the groin and the eyes in targeted combat.

I loved the descriptive text in fallout,1 and 2 when you got critical hits. Like for example, "you smash in the guys head with your sledgehammer as easy as a wet paper bag".

I loved in fallout 2 how I won the boxing tournaments with a guy who didn't use unarmed, but instead took buffout, then nut punched them until they got knocked out, as causing them to miss a turn counted as an automatic win.

I loved doing the same thing as above, but managed to win the tournaments without throwing a single punch by using the jinxed trait and ending turn until the boxer critically failed and knocked themselves out.

I love the jinxed trait in general and fighting a gang and having guys shooting themselves, or dropping weapons or whatever.

I love how in fallout 2, you can go bang the Bishop gang leader's daughter, leave her room and get attacked by Mr Bishop, shoot your way out of there, then go bang his wife.
And to top it off, they acknowledge if you didn't use a condem with the end slide and how the new Bishop son was unlike the rest of the family and loved to explore the wasteland.
And to make it even better, in new Vegas you can meet a man on the run from the new Mr Bishop and he says how he knows the wasteland like the back of his hand, making the new Mr Bishop being canonically the son of the fallout 2 protagonist.