I've mostly been playing the modding game for TTW
It's a dangerous game, because it's very hard to stop once you begin - especially for these games - as there are literally thousands of potentially interesting mods.
But I'm pretty educated on modern Fallouts and what I think aids the experience in a meaningful way. So, I haven't gone overboard - and have landed at around 86 mods, with a good mixture or visuals, gameplay, audio (radio) and so forth.
I can't really tolerate the default NPC faces, for instance - and you really need a few low-hanging fruit like texture packs for the environment.
For gameplay, I absolutely require a decent VATS alternative - as I was never a big VATS guy - especially in FO3/NV where it's more like cheating.
There's a great bullet-time mod that incorporates all the VATS related feats in meaningul ways - and I love how it can auto-activate as you aim, but only during combat - so that you can't cheese it as a sniper and so forth. It costs AP while active - so you have to be very aware of your pool and it doesn't feel like cheating like VATS. Without it, combat is a little too fast and awkward for my tastes.
This is one area where Fallout 4 is far superior, imo.
Modern Fallouts are also way too easy almost no matter what in Vanilla - so I need certain mods to make combat more engaging and enemies feel like a threat. I'm using the popular JSawyer mod (mod from one of the lead Vegas devs IIRC) combined with the excellent Bleed mod. These two combined means being shot is extremely dangerous - and you can't cheese things that easily.
For instance, I was just in a firefight with but two Raiders. One of them had a sniper rifle (I had my 10mm pistol) - and another was melee. So, my tactics were to take care of the sniper first - so I could safely engage the melee girl.
So, I finally get him down (very low health) - and I breathe a sigh of relief.
Then, the damned melee runs over to the dead guy and picks up the sniper rifle and shoots my head off
Other stuff like sprinting, grenade hotkeys, backpacks, immersive UI elements - and so forth will all help the experience without breaking anything.
For radio, I just need the Old World Radio mod - which brings a ton of 50s style spooky and sci-fi horror, which I find to be the perfect companion for exploring the vast landscapes.
Anyway, I forgot just how fantastic the Fallout 3 beginning is. Beth always made great intro levels, but FO3 is my favorite - and I think it's a nearly perfect combination of elements. It gives you just enough to work with to make it feel like you're actually growing up in a vault - but not so much that it feels like a needlessly long drag.
A wonderful concept as an introduction to the Wasteland. It makes that first step into the open world particularly impactful.
Anyway, I think this will be my game of choice for the forseeable future.