The problem about Fallout 3's replayability is that it's cartoonish evil.
I wanted to play as an evil person, but rather than the 'the end justifies the mean', it's 'lol why you should do it? It's evil!'
When I sided with Caesar, it was evil (slavery, sexism, bla bla bla,) there were an actual point to it. Caesar explained very well why the NCR can't do anything good in the Mojave or in any way, why they aren't democratic, which actually convinced me to join him after I planned on a Mr. House play through. You can be a c*** in the game, but there were good reasons to join the evil side.
Now, it's about Fallout 3's evilness.
Blow up Megaton... or don't. Why should I blow up Megaton? Is it a danger, does it do anything wrong? Nope. The master mind of the explosion Tenpenny is like 'Because I don't like it.'. What?
Join the Enclave.... no wait you can't. There is one faction, the Brotherhood of Steel which really should be 'love for technology, don't give a shit about anyone else!' mentallity, but in Fallout 3 they are angels, coming to save us all from the mutants (who are humans!!!!!!!!!!!! green humans and has no say in Fallout 3, though being the second antagonist. (why is there antagonists in this game, it's and RPG. You decide the god damn antagonist)).
The only way you can join the enclave is by exploding the citadel, for no reason, or destroy the water by posioning it. President Eden has no philosphy, nothing to say, but to be evil... for evil's sake.
This game got be introduced to the series, but it ended up being my second least favorite (i have not played Fallout: Brotherhood of Steel yet, and don't plan on it,) so it's pretty much like:
1: Fallout New Vegas
2: Fallout 2
3: Fallout 1
4: Fallout 3
5: Fallout 4
I shall play Fallout Tactics at one point though.
//I know this was a rant, and kinda went off topic, but I really needed to say this. Thanks for your time.