describe the gameplay more please 
one of the amazing things about the game is that you can play a lot of different ways and they're all fun. I explore like crazy and take each dungeon (scary abandoned buildings and subways in this game) really slow. The dungeons can be really tense. You don't know if it's just a few measly raiders with bats around the corner, who are no match for a shotgun to the face, or some well armed guys with shotguns, missiles, and whatever else. Sometimes there are traps laid out, sometimes the place is yours for the picking. So I go about it stealthily to conserve ammo and supplies...like what a real survival horror game might have you do.
Likewise, I love creeping around outside, but once again, you could see some hideout that looks free to raid, only to find super mutants with heavy artillery just around the corner.
The goal of all of this is to get all kinds of loot to survive, of course. Even just useless shit you can sell for caps, since money can be relatively scarce. Though that's nothing new to rpgs, it's incredibly compelling in Fallout 3 since nuked DC is an interesting place to be in.
and that's just the freeform aspect. The actual quests are all pretty interesting and time consuming. My only complaint is that your choices are not morally ambiguous, like in the Witcher. Though it blows away the dialogue trees in Oblivion, KOTOR, Mass Effect, etc., it's still mostly cut and dry, good or evil.
