simple
gameplay- good mix of stat based and skill based + many improvements.
1st person perspective- increased immersion, control & fun.
exploration- goes hand in hand with first person perspective- finding a secret area is far more rewarding in 1st person, and even small things like finding a stimpack under a bed.
story and NPCs i have no say in, since i did not complete FO1, but many have said new vegas stands up well to the old fallouts.
if you ask me fallout is the only series that has actually improved with the advances of the industry. turok, tomb raider, elder scrolls, duke nukem, tenchu, final fantasy and many more.......what happened?
Gameplay, nope, less skills and SPECIAL is near meaningless in FO3 and only slightly better in FONV.
FPP, nope, I don't care about "immersion" that gets tossed around the gaming scene way too often.
Exploration, if I wanted a sightseeing tour I'd play Saints Row, Just Cause, GTA or TES.
Story and NPC, yes, NV stands up well and is even improved in a lot of areas, but considering NV has to stand awkwardly next to FO3 it gets dragged down with it.
Improvements?
No.
Fallout didn't only take a step forward, it took a couple of steps to the side and dunkenly fell backwards a couple of steps. One step for FPP, another for exploration and combat heavy gameplay, then it took one step forward in graphics, but one step backwards because of the loss of a map node system, another step backwards due to the loss of several skills, another step backwards due to the streamlining of enemy compass and quest markers, another step backwards due to SPECIAL being dumbed down and another step backwards due to the horror that is Gamebryo and how the AI svcks in it.
So from my very crude count, 2 steps to the right, one step forward and 5 steps backward.
=
Did not improve the Fallout series.
Just cause it's changed in graphics, been turned into an FPS and has tons of meaningless exploration does not mean it evolved, simply that it changed, and for a lot of us it changed for the worse.
[edit]
Another couple of notes:
* Ghouls look like burn victims.
* Super Mutants (in NV) has way too clean skin and barely any of them have any cancerous growths.
* No fat people or little people.
* Old people looks like models if you take off their clothes.
* Lasers now turns people into ash instead of slicing them apart.
* Wattz series is completely gone despite having been reimplemented by modders in both FO3 and FNV.
* No Gamma Gulp Beer or Root Beer, just damn Nuka Cola variants all over the place.
* Radiation is ridiculously nerfed.
* Drug addictions are a joke.
* Too many perks and too many crap perks.
* Bullet sponge enemies.
* Bad combat balance.
None of these other things are improvements, removing, tweaking, streamlining and nerfing features is not an improvement.