A great RPG with just a few problems.
Once you leave Vault 101, you decide what you want to do. You could follow the main story-line, or you could drop the whole thing completely and explore the Capital Wasteland. Players can also level up their characters however they like whether it is making them skilled at guns, or speech, or medicine. The game makes the player feel that they need to survive because weapons and armor gradually wear down over time. Dialogue options with other characters are very immersive.
Where the game really shines is exploration. Finding small towns such as Grayditch, and Megaton give a real sense of atmosphere. Exploring the Washington D.C. district is also interesting. Side quests can usually go in many directions which is pretty great. The same cannot be said for the main quest-line. It is not terrible, but there is not as much choice as there is in the side quests, until the very end of the story-line.
Fallout 3 does have a few issues. First of all is the glitches. The game can crash occasionally, so save often. The game can also lag a lot unless you turn off the auto saves. The lagging happens more often if your character is a high level. The glitches appear a lot in the dlcs. Secondly, there could also be more side quests, and settlements. I strongly recommend against buying against the Game of The Year Edition of this game because the glitches are even worse. It got so bad that I could not progress my character past a certain point in the map because the game kept crashing at that spot. The regular edition has a patch that makes this problem less frequent.
Fallout 3 is a great game with a few minor problems. As long you have patience for occasional glitches, then you will have a great time in the Capital Wasteland.