the only real politics Fallout 3 had was in the Pitt DLC and dealt with power politics but ultimately didn't go much further than that because of AAA games not wanting to piss off potential players
NV explores the entire fucking political spectrum, not just Mr. House style Libertarians, it's just that Mr. House and Yesman are the most fleshed out because the game was rushed and we only get about 33% of the final product and Mr House was the first on the to-do list so it appears like it leans his way, however the NCR is the typical corrupt liberal democracy with the redeeming factors of being flexible enough to face any storm while Caesar is on the surface a fascist but is really just a Marxist accelerationist who's playing the bad guy just to speed up the NCR's progress towards overthrowing its liberal democracy in order to face a real threat(he literally mentions dialectics and Marx and in the cut content you go to Flagstaff to help a slave revolt at which point Caesar reveals that was his plan all along and then kills himself so you become the paragon of the wasteland as he was the final boss, cool guy)
Fallout 4...... ugh..... it dealt with some cool themes like the idea of whether Synths are actually people, things, or a creation whose master left it to rot in a world not ready for it(straight from Frankenstein) but never ever touches upon this other than hinting at it. The story is so bland that whereas Caesar went on a 50 page long monologue about how he needs to be evil so that good can triumph over him, when you ask Father why the institute is the big baddy he literally responds "you wouldn't understand". HE LITERALLY JUST BRUSHES YOU OFF INSTEAD OF EXPLAINING THE DRIVING FORCE OF THE GAME WTF.
Fallout 1 is more about looking at Maslow's hierarchy of needs in a post-apocalyptic environment, ie the driving force of the game is the water chip cause you know water is important, at which point greater needs arise(The Master) and you focus on that instead and despite being the big brave good guy you still get fucked cause hehe survival requires control of ignorance in a controlled environment, no variables allowed. Plus the Master. Ohhh boy that guy is the best damn villain of all time hands down, as in he's actually the good guy but has flawed logic, he just wants everyone to survive and he thinks he has the best way, but when pointed out that A: this is just fancy eugenics, and B: his new race isn't so great after all since they're all sterile, he realizes his plan has no point and therefore just gives up because he turned out to be the bad guy.
Fallout 2 is just a massive critique of the US, as in shady CIA stuff, literal black helicopters flying around doing shady stuff, everything is actually just a controlled experiment because lol knowledge, despite there never being an application for said knowledge, and massive eugenics which while sounding good on paper only benefits a very select few and they just happen to be in power.
TL;DR: Old Fallout more cynical and in depth, modern Fallout tries to pander too much and while having some good core themes to work with never fully develops their potential with the exception of NV whose shallowness comes not from bad devs but the fact 2/3rds of the damn story is missing due to deadlines.