Everything an RPG should be, and more!
Let me start with the flaws, well there are none really because a big chunk of the glitches and bugs were fixed in an update and the game has a slow start. After leveling up a bit and getting some good items, this game will be great, so I suggest putting the game on very easy(for the first playthrough) until about level 10, then choose what you would normally play on. Also combat kinda sucks outside of V.A.T.S.
Fallout 3 has a huge open world to explore and tons of quest between Main(story), Side(achievement), or Unmarked(just for rewards), you can easily get over 60 hours of gameplay on this game. The quest are fun and don't feel like a chore to do. One of my favorite parts of the game is getting NPC companions like Charon who is a ghoul who you can get a contract for from the underworld, Dogmeat who is well.... a dog who follows you, aids you in battle, and finds ammo for you, and my favorite FAWKES! Fawkes is found in Vault 87 by the G.E.C.K. and is the only Super Mutant who isn't hostile and the only time I've seen him die was against a Super Mutant Behemoth. Another thing I love is the amazing and insane weapons. The Rock-IT-Launcher will shoot anything from useless junk to teddy bears at people, The Alien Blaster found in a spaceship, also possibly the best weapon in the game, shoots blue rays that instantly kills almost anything, Fat Man which shoots a Mini Nuke, and the most insane weapon since the B.F.G. in Doom, The Experimental Mirv. The Mirv shoots EIGHT F-ING MINI NUKES AT ONCE!
Some final notes, if you don't know what platform to get this on well the PC version is the best if your PC can run it since it has the exclusive G.E.C.K. which lets you edit the entire game and has cheats to make the game more fun, and if that wasn't enough the PC version also has achievements because it is a Game for Windows. The 360[and PC] version has DLC that the PS3 won't be getting so PC>360>PS3. I HIGHLY RECOMMEND BUYING THIS GAME TO ALL RPG/SHOOTER/ADVENTURE FANS!