Copypaste from PureZC:
There were times that I felt that it really was "Oblivion with guns." It can be, but it's so much more, as Bengal said so eloquently. Whereas Oblivion has you exploring a medieval world and attacking random encounters with wolves and crabs and trolls and skeletons, Fallout 3 has you randomly killing raiders and super mutants and mirelurks and stray dogs and molerats and bloatflies and such, only you have guns. :shrug: You can explore caves and tiny vaults and farms and burnt-down buildings and real vaults and cities and towns and libraries and such.
The DLCs are pretty good, actually.
Operation Anchorage has you locating a Brotherhood Outcast outpost, where they ask you to enter a war simulation so that you can unlock a vault of goods they found. The simulation pits you against the Chinese communists in Alaska, where much like a combat simulator, enemies and their loot vanish instead of being lootable. It's more like an FPS than an RPG there, as you have no real inventory. You get to scavenge for 10 briefcases of intel, which give you a neat perk if you get all 10. The loot in the vault is very worth it.
The Pitt, admittedly, I have never played. It's okay, from what I hear. Interesting new items and weapons and armor. It's more of the same, I guess.
Broken Steel: Now this is where the meat and bones is of the DLCs. It extends the level cap from 20 to 30, (Awesome. Just Awesome.) and when you would have beaten the game, sans DLCs, you get to continue with more quests and an expanded main plotline, resulting in a greater sense of self-worth. 😊 Pretty darn good DLC. Definitely a must-have installed.
Point Lookout is a nice one too, I guess. It adds its own smaller overworld to explore. The weapons and armor are actually more victorian than industrial or futuristic, as are the enemies. The area is slightly less destroyed than the Capital Wasteland, and you'll see plenty of trees and shrubs around. It's pretty neat. A bunch of new quests and NPCs to interact with. You get to make moonshine. 😃
Mothership Zeta is a kickass DLC, if only for the loot that you get, and the ending and end result of it are pretty darn awesome, I guess. (There are mods that expand even that.) You get abducted by a spaceship, locked in a jailcell, and have to escape, and beat up the guards. (With your FISTS.) The weaponry you get to pick up is literally out of this world, from laser guns to alien blasters to alien cannons, to the awesome drone cannon. I picked up a Plasma Pistol that I liked so much that I didn't want to switch away from it. If you have infinite carry weight, and get to keep all the alien blasters, you will get a MASSIVE haul of caps when you return to the mainland.
Bah. I always hated carry limits anyway. But I guess they're a necessary part of the game. :-/