3 just copy/pasted then crapped on Fallout 1 and 2's stories.
It's gameplay is the same. Fallout 3 is just Oblivion with guns, cliche I know but it's true.
I'll add that I loved it when I first played it and knew nothing of the series. The world is amazing and the game is a metric ton of fun. It has massive replay-value since it takes forever to explore the entire map and every location has something neat about it. I don't hate the game it just has insanely lazy writing.
That's exactly my take. Fallout 3 was my first fallout experience and I was awed when I first played it. I did like 3 play-throughs and then I got New Vegas. After that, I simply couldn't touch Fallout 3 anymore LOL.
What I like about the Fallout universe (also coming from TES), is that it has this huge world you can explore AND you can use guns! I love FPS games, but I prefer huge world exploration games, like the one Beth created for the TES series. For some reason I thought Fallout was just some silly linear zombie shooter... OMG I was never more wrong in my life! (well maybe the time I got married... but that's a different story hahahaha)
Seriously though, I would get both games! Fallout 3 has a cool Urban setting and it was a blast to run around a destroyed Washington DC, while New Vegas is a bit more gritter and feels like a more "grown up version". Your actions have consequences and you will affect the Mojave in ways you can't imagine. Plus, the New Vegas DLCs are 100 times better than the FO 3 ones.
How serious are you about playing these games if you are already asking for exploits or glitches? o.0
Leveling system: You earn XP by completing quests and shooting creatures.