I was hard on poor Fallout 3 when it debuted. I lambasted it for weak storytelling and poked fun at the gameplay in my comic, although I managed to have a lot of fun with the game despite my rantings. Still, I always found myself wishing the game was more polished, more diverse, more realistic and with more depth. All of this is now fixed, and developer Bethesda didn't have anything to do with it.
I have been installing a lot of mods for Fallout 3, to the point where the Fallout 3 I'm playing now barely resembles the one I bought. The world looks different. (A mod to add green grass and trees, another to remove the pervasive green tint and make nights darker, and a few more to overhaul the textures in places.) The characters look different. (Mods to overhaul the bodies, add hairstyles, and revamp the face textures.) It sounds different. (A mod to put in the music from the original Fallout games.) It plays different. (A mod to require the player to eat, sleep, and drink to survive.) It's less annoying. (A few mods to make the interface more friendly to the mouse-owning PC players with high-resolution screens.) And that's just my short list of "must have" mods. There are another dozen or so novelty mods, extra weapons, gameplay tweaks, and aesthetic changes.
Sure, the mod community has been around since long before Fallout. You can still download mods for the original 1993 Doom, and it was by no means the first to get this sort of love from devoted fans. There was a bit of a modding slump there for a few years. For a while I thought that modern game engines were just too labor-intensive for hobbyists to tackle, but they have proven my fears wrong in a big way. I've never seen the mod community this large, prolific, skilled and diverse. Replacing a modern 10,000 polygon monster is far more challenging than replacing a bunch of little 256 color bitmaps, but people are doing exactly that - and delivering solid results.
As of this writing there are over 6,600 mods available in the Fallout 3 Nexus, and that number goes up every day. All of them are community-made projects. Some are huge and ambitious. (Like a complete game-balance overhaul.) Some are... modest. (Like someone posting, "here is a savegame of my character so you can play as him hes awesome and his name is logan just like wolverine, get it?") So you'll have to sift the list a bit, but by looking for popular downloads you can find gigabytes worth of incredible enhancements.
Many of them deliver professional-grade quality, showing off genuine talent on the part of some truly dedicated fans. For example, there are multiple mods to replace the male and female bodies, and they look better than the bodies that shipped with the game. If if you're picky, you can choose how big you want the breasts to be or how much wang you want to see during your post-apocalyptic adventures in Washington D.C. Do you want to ride a motorcycle? Fly a vertibird? Swing a lightsaber? Watch girls pole dance? Play as a ghoul, or a child? Be hunted by a robotic terminator? Play a real-time strategy minigame where you establish and defend a settlement? Make your own radio station from your mp3 collection? Be able to capture existing NPCs and sell them into slavery? Use night vision goggles? How about et cetera? It's all there, and more.
This is not to say everything is perfect. Mods often conflict with each other, or cause crashes, or lead to visual glitches, or break gameplay elements by introducing unintentional exploits. It's a complicated hassle, but the payoff is well worth it. It's like getting a free game. Or a couple of free games. Games which have been designed to cater to your specific tastes.