I've only played Fallout 3 and 4. And out of those, I greatly prefer Fallout 4. Aside from the dialog options and such, I though Fallout 4 improved in nearly every aspect.
- Much better combat, so you can play without always having to use vats as a crutch, now that the RNG bullshit is gone. The feel of the guns are much better.
- A better designed open world (commonwealth was more fun and interesting to explore, with more variety than the capital wasteland)
- Better graphics all around (this one is sort of cheating, but still)
- Removal of that stupid karma system (losing karma when nobody can see you was bullshit), weapon degradation (has no place here),
- adding the ability to actually run in game
- adding mod support on console, adds a lot of longevity to the game
- Looting felt much better and quicker due to the menu that pops up, not having to open a seperate screen
- conversation occurring in real time, time doesnt stop anymore.
- actual factions to ally or make enemies with, when Fallout 3 had none.
- No more heaps of useless junk items, every little item has a purpose and can be used to build something.
- A better and more vibrant color palette, no more puke green filter
- Unpopular opinion, but settlements. They were actually pretty fleshed out so you could go ham with them. Though I understand, not everybody has the patientce to build something for four hours.
The only misstep/step backwards I would say, was limiting the dialog options to just 4, and only having one word despcriptors for it. And there werent many options to end things peacefully, you were always pushed into combat.
Unlike others, I was perfectly fine with the perk system and voiced protagonist in Fallout 4 as well.