Fallout 1 & 2 = Classics that feel like it. Slow. Boring.
Fallout 3 = The start of modern Fallout. A bit jank, but fun story, and the sweet spot of RPG that's perfect for newbies and RPG autists alike.
Fallout New Vegas = Obsidian showing why they lost the license. Shit characters, shit story. Adores by trannies for some fucking reason
Fallout 4 = Visually improved, gameplay dumbed down. Leans more into being an FPS than an RPG.