Think post-apoc survival movies. Anything from environmental/map changes, to armor, to weapons, to aesthetics, to quests & mechanics. DUST excluded here, as much as I'd like to play it I also like to be the Courier and play the main quests.

Looking for things like mismatched armor, jury-rigged weapons, bleak lighting, rubble everywhere; a more bleak, harrowing, harsh and unforgiving experience.

For ruble definitely apocalyptic mojave,new vegas post apocalyptic and rusted highways
For armor i would go for spice of life,wasteland soldier,Couriers Cache (includes some weapons like homemade flametrhower)
For weapons some homemade ones are included in project nevada
For mechanics i would go with realistic weapon damage so you could feel woulnerable most of time
And of course for music i would recommend fallout 1&2 ambient music or DV's Custom Soundtrack
Also for pure immersion i recommend mojave sandy desert, nevada skies,
For character scarred race surgical scar plugin (so you can actually look like you were shot in the head) and killing karma reward (now killing bandits and ghouls in self defense wont make you mojave saint)

Well thats what came to my head pick what you wan and have fun

For homemade weapons/variety, I recommend this: http://www.nexusmods.com/newvegas/mods/53689/?

It's not amazing quality, but there certainly a lot of them and they aren't terrible. IT adds a lot of guns to the level list so if you see an enemy with a cowboy repeater, there's a chance it could be a darkwood cowboy repeater or a nickel-plated cowboy repeater(each differ in stats). There's also some crafting recipes like a few rechambering guns(change which ammo it uses) and some ways to "mod" the gun(s). I consider it a necessity to have this mod just because it adds variety to the guns. I got so sick of every enemy using the same guns.