1, 2, Tactics, and BoS are all pretty tough to get into because they're fairly dated.
Start with 3, play the hell out of it. Then, important, TAKE A BREAK. Not enough people went into NV without a break from 3, so they got Fallout-outed and blamed NV for it. After a month or two, play NV. NV is the perfect combination of old school Fallout with 3's mechanics. You won't quite understand What I'm about to say unless you know a very good amount of the series (as in, you've read the Fallout Bible): Fallout 3 is Oblivion with Guns, NV is Fallout 3 but Fallout. Nothing wrong with 3, fantastic game, but it's significantly less Fallout than NV is. 4 will likely align closer to 3 though.
I just hope to god they let Obsidian write the game. 3's plot was dreadful and had a bunch of flaws in regards to the rest of the series.
Last thing, play all of the DLC from both The DLC made Fallout 3 what it was, and it improved NV steadily (and also includes one of my favorite DLCs if all time).
You should check out my YouTube channel, The Golden Bolt! I review all types of video games, both classic and modern, and I also give short flyover reviews of the free games each month on PlayStation Plus to tell you if they're worth downloading. After all, the games may be free, but your time is valuable!
