Blood Puppy hit the nail on the head regarding the replay of the the earlier Fallouts when compared to 3.
My first playthrough of FO1 was a pretty rough jack of all trades character, I tried to be good at everything and struggled horribly to finish it. I also didn't quite understand the perk system and how sets of them meshed with each other, I just sort of picked them because "ooh, that sounds cool, so does that one!"
My second playthrough I was much more focused on combat, pumped a lot into big guns and energy weapons, figured out how to maximize my ranged damage with sharpshooter, sniper and such, I even posted a character creation guide somewhere on the net showcasing this character way back when. (I still have the old .doc if anyone wants it for a laugh
)
Then I tried using INT as my dump stat and laughed hysterically at my crippled dialogue choices.
I tried a melee only fighter, I made stealth/infiltration experts, I literally cannot count how many builds I played through Fallout 1 with.
Fallout 3 on the other hand...
My first playthrough was my pretty typical "goody two shoes hero" I sprinkled skill points across the board willy nilly trying to get a feel for how things worked. By all rights I should have screwed myself because I ignored science for a very long time, by the time I realized how valuable it was I was level 12 or 13 and had less than 30 points in it. By the time I beat the main quest it was at 100 anyway.
The bobbleheads and multiple skill books skew the importance of carefully choosing your skill point placement as you level up.
SPECIAL stats give you extra benefits and discussion options if high enough but I've yet to find a negative result for skimping on one. INT 1 is just a talkative as INT 10?
I tried to replay FO3 and despite being evil instead of good the game is not a significantly different experience. I had more or less assumed that being evil would have prevented Talon company from being hostile by default, nope, they still aggro me for breathing. Is nuking Megaton a game changing experience? Nope. Tenpenny tower offers the same perks, and you don't even cut off your chances of finishing the survival guide. Let ghouls into Tenpenny tower? No sweat, they'll still let you live there once the dust settles.
I'm not saying that the player needs to be destroyed for making "bad" choices but FO3 really makes you feel like your choice doesn't matter because nothing you do really impacts anything.
If your choices change nothing there really is no new experience from a replay. Other than making a different looking character? Oh wait, nevermind I can go see the plastic surgeon and make myself look different anyway. I've tried twice now to replay FO3 with different builds and both times gave up from boredom.