Yes, Mass Effect is more like playing along with a movie. It’s more cinematic and sweeping in its story line than Fallout3.
Graphics-wise, I’d say both do an outstanding job. They are at opposite points of the spectrum, however, in that ME is set in space, so you have all the futuristic eye candy of nebulae, stars, planets, space stations, etc. The mail station has a very sterile feel to it, as does your ship. On the other hand, Fallout has somewhat of the same overall feel as Bioshock in that here’s a world that’s gone to hell. Everything is run down and dilapidated. And it has those elements of what the “future” would look like from the perspective of the early atomic age: the ruined cars all have the swooping taillights and are as “big as whales.”
You get far more interaction with the world of Fallout 3 than you do with Mass Effect. In this regard, Fallout 3 is very much like Oblivion (notice the general “nothing is coming to kick your ass” background music is exactly the same), and I would expect this since both games come to us from Bethesda Softworks. While ME spans a good chunk of the galaxy, you are limited to small plots on each planet, and (at least in my play), everything is always in the same place every time. This means evil doers are predictable with each game play. To an extent, the same thing applies to Fallout 3, but in my op., there seems to be a more robust game AI with Fallout 3.
Both games are outstanding, and are a good value as they will provide many many hours of game play. You couldn’t go wrong with either of them.