I don't already know this. I literally know next to nothing about video games.
Why would I like it?
If you like
Red Dead, liking
Fallout 3 is almost a guarantee. They both emphasize big open-world exploration, with tons and tons of stuff to do. The main differences are in setting and POV:
Red Dead is third-person and set in the old west,
Fallout 3 is first-person and set in a post-apocalyptic world.
Fallout 3 definitely has the kookier sense of humor... society has evaporated, so it's more people giving you odd and kooky things to do than
Red Dead, which tries somewhat harder to maintain some illusion of realism in between the humor. Heck, they even both have a similar system of special ability for shooting:
Red Dead has Dead-Eye,
Fallout 3 has V.A.T.S.
I could spend pages going over similarities and differences, but best you just watch a video review (below). If it looks interesting to you, give it a try. It was released in 2008, and there's been a (less impressive) sequel released since then, so you can get it for really cheap... like 20 bucks. Trust me, I play lots of video games, and this will almost certainly be money well-spent for you.
(BTW, the conversations with Harold the Tree in
Fallout 3 are some of the funniest dialogue I've ever seen in video games).
Oh, and one more note sort of technical note: there have been five DLC releases for
Fallout 3 that add more missions and storyline and such to the game. If you do end up getting the game, the only one of these that's really essential is
Broken Steel, which allows you to explore and do other missions after the main storyline is complete, as opposed to the game just ending after the main story without it, necessitating re-loading a previous save if you want to keep on playing. It also raises the level cap to 30, adds new "perks," and a whole other storyline to play through. The other four pieces of DLC are fine and all, but
Broken Steel is the one to get if you don't want to burn your money getting all five of them. It cost 800 MS Points ($10) to download it through the X-Box Live Marketplace when it was first released, but the price may have gone down by now, I dunno.
https://www.youtube.com/watch?v=mCEThrx6qqY