Fallout

TLDR either start with Fallout 1; or Fallout 3 or NV. If you start with 3 or NV you can play the opposite game second, or Tale Of Two Wastelands to combine them. Don’t start with Fallout 4 since it relies most on knowledge of the series and because it is hard to play 3 or NV after experiencing 4’s engine upgrades.

Your biggest hurdle with Fallout 1 & 2 would be less that they are dated, and more that they are in an entirely different genre. If you are coming from Borderlands, then a top down, turn based combat, dialog heavy game might not be what you want. These are excellent games and I highly recommend them, starting with Fallout 1, but some people just can’t adapt to the gameplay.

Fallout Tactics is a spin-off that can very much be skipped unless you’re a completionist or love real time tactics games. It’s non-canon, despite a few oblique references in later games.

Fallout 3 and Fallout New Vegas. The great debate. The Todd vision vs the Obsidian vision. Opinions are of course subjective, except for mine, which is objective and New Vegas is objectively better.

I joke. I do like New Vegas better but I appreciate the writing style. It has a tone closer to the classic games, a coherent set of factions, and a blank slate player character. Fallout 3 has more locations that are novel and have bizarre stories attached to them, but as a whole the world feels disjointed- like different people were responsible for writing different areas and only occasionally talked with each other. It’s a very kitchen sink approach to adding every possible idea in.

Fallout 4 is more of 3, with an even more pre-conceived character and fewer options to make a unique personality. Stripped down dialog choices and a voiced main character. However it is the prettiest game, has the best first person shooting of the series, and an absolute buttload of mods.