Fallout 3 starts, strangely, with your character being born. Enjoy this new life scenario, as it will be one of the very few you see.
You get to find out what you're going to look like when you grow up (you actually get to decide this). Then, you get to be a toddler. More developing yourself. You learn that you are in a vault. You take a test. Some bad things happen, and you have to leave.
The second you step out of the vault, you get feelings of awe. Then you walk around for a minute and begin to understand just what you're seeing. This used to be Washington D.C.
Visually, Fallout 3 is fantastic. It's hard to notice when you're in the vault, as the graphics all look pretty much the same, and if you played The Elder Scrolls IV: Oblivion, they look very familiar too. However, when you get out, you get to see some of the artistic design. You see how the developers have taken real buildings in Washington D.C. and ruined them in a believable way. The textures on the land and monuments look great. The NPC visuals could have used some work, but they're passable by all means.
Fallout 3 also sounds great. You get some ambient tunes occasionally, but most of the soundtrack is old 50s tunes coming from either radios in the game, or from the radio on your Pip-Boy (more on this later). The songs can make you feel a bit unusual, as you may tend to try to place together what the buildings and landscapes looked like before the bombs fell. The sounds effects and voice acting are very well done, as well. Grunts and threats from Super Mutants are amusing, and the sound of a Radscorpion or Deathclaw coming your way can make you jump out of your chair. The voice actors for the NPCs are all shockingly believable.
There's a lot to say about the gameplay, because there is so much of it. The Pip-Boy has all the information your going to need. However, at first glance, it can be a bit intimidating. You can use it to fast travel to places you already been, look through all your items, check your quests or your status, heal yourself, and many other things as well. After a few hours of gameplay, it comes naturally.
The shooting mechanics are very well done considering the game is billed as an RPG. The interesting thing about this game is that you don't have to play it in any particular way, though. For instance, if you want to use melee weapons for the entire game and not shoot anything, that is an option for you. If you would rather nuke and blow everyone up, that's an option too. Or maybe you'd like to sneak up on all your enemies and take them out in stealth mode? That too is an option. In some cases, you can use your intelligence rating to avoid fighting at all.
Exploration is a big part of Fallout 3, as well. You can technically play through the main quest without doing anything extra at all, but there's so much to see and so many interesting people to talk to, that odds are good you won't do this. If you were to play the game straight through, you would never realize that there is an area full of people who think they are vampires, or a seemingly innocent town of cannibals, or a vault full of insane people who all think their names are Gary. There's even a super hero and his nemesis.
Leveling is a big step in the right direction for a game developed by Bethesda. Most Bethesda games work on a leveling system that rewards you for using certain abilities. For instance, if you wanted to be able to jump better, you would jump a lot. However, Fallout 3 uses a leveling system similar to the original 2 Fallout games. You gain experience, then you gain a level. When you gain a level, you get one perk, and then a certain amount of points to add to your skills. The placement of these skill points and the perks are important, because they determine what kind of character your vault dweller will be. Your skills vary from personality traits to battle related, so you have to be careful. If you create a character who is very good at barter and speech, but has no weapon or medicine skills, you may find yourself struggling to stay alive. However, if you ignore things like speech, lockpick, and science, you may find that you are unable to access areas you really want to go.
As for how long it lasts, it really depends on how you play it. If you play through the main quest, you can finish it in 20 hours or so, possibly less. Most people will not do this, though. Adventuring in this game is addictive. If you decide you want to try to visit every area, the game can last as long as 60-80 hours.
Now, the Downloadable Content.
Operation: Anchorage is more or less a battle simulation. If the more social aspects of the game were your favorite parts, I'm not sure I can recommend this. Keep in mind though: the spoils are great.
The Pitt is for Fallout fan who likes to make decisions. There's still combat here (and some of it is actually pretty challenging depending on your decisions), but the focus is on what you say.
Broken Steel is flat out necessary if you're going to play Fallout 3. It boosts the level cap from 20 to 30, and expands the ending (the original ending is universally known for being piss poor). The new quests are fun, and they are all located in the D.C. Wasteland, rather than an entirely new area.
So overall, I highly recommend Fallout 3. Even with the release of some great games in 2008 such as MGS4, Prince of Persia, Persona 3 FES and Gears of War 2, I still believe Fallout 3 was the best game of 2008. The only gamers I can't really recommend it to are those that are bit squeamish to gore or don't enjoy dark humor, as this game has both in great quantities. There's RPG elements, first person shooter elements, and adventure elements, which should be enough to please just about any gamer.