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Yes, by now it's semi-old, but even today, via Facebook feed of the Vault wiki, I learn things I never knew, and I've played the game through several times, with hundreds of hours. Most games you play that much, you are looking at serious repetition of 10x the same scenarios or more. Exploring and doing everything, I probably only found the same areas or did the same quests 3 times, each with different builds.
Anyone who has used the vault as a resource knows that just based on that, the game is massive, like no other game has ever been, and probably ever will be. New vegas impressively had about 75% as much content, and skyrim probably had about 75% as well. And you can tell the difference based on wiki pages and articles available between the games. Find any other game with as many articles denoting all the different items, gameplay mechanics, areas, quests, npcs, etc. You can't, it doesn't exist. It's possible it never will, though I hope that's not the case.
I know bethesda has a lot of haters, but F1 and F2 were really very small games, though good, compared to F3 and it's just easily the king of the open world rpg. Onto the list...
2. Mysterious stranger
3. Tenpenny Tower
4. Reilly's Rangers
5. Harold in Oasis
6. DC post-apoc... the mall, the washington monument, lincoln monument...
7. hacking, lockpicking, speech checks, skill-based dialogue options
8. reverse pick-pocketing to change armor and blow people up
9. 3 dog
10. Tranquility Lane
I could do this ten times and not run out of cool stuff about the game. If for some reason you haven't played it... don't let time turn it into one of those old games that are awesome but impossible to get into. As someone who's always gaming, I've still missed out on a lot of good rpgs that I just didn't know about 15 years ago.