Oh dude... you gotta get these Fallout 3 mods:
Mart's Mutant Mod:
Marts Mutant Mod - RC 6 at Fallout 3 Nexus - Fallout 3 mods and community
* Every creature and NPC is unique with its own stats, size, confidence, health, damage and even skin (texture)
* Creatures and NPCs suffer improved wounding effects such as visible bleedng and statistic penalties
* Creatures and NPCs can loot the corpses of fallen enemies, afterwhich you can find this loot if you kill them
* Creatures and NPCs have improved behavioural AI based on class -- in any given group some may be aggressive towards you, some may be ambivalent, and others may avoid you outright.
* Configurable increased spawns allow you tailor how many creatures and NPCs spawn in the game at any given spawn point
* Improved faction system to better reflect inter-faction relations and ensure the player isn't the center of the universe
* New creatures and NPCs to add variety to the wasteland -- all hand-crafted with their own stats, abilities, loot, weapons, textures and in some cases scripted AI behaviour.
FOOK2 (Fallout Overhaul Kit)
FOOK2 RC v1-1 Beta 2 at Fallout 3 Nexus - Fallout 3 mods and community
FOOK2 is a complete overhaul of FO3. It adds hundreds of news items (weapons, armor, clutter, food etc.), has high quality retextures for many vanilla items and many new gameplay features.
On top of this are all items completely rebalanced and fully integrated into the game and it has also support for ALL DLC's.
Fallout Mod Manager
Fallout mod manager at Fallout 3 Nexus - Fallout 3 mods and community
Small program to manage your mods. Absolutely priceless.
FOSE (Fallout Script Extender)
Fallout Script Extender - FOSE at Fallout 3 Nexus - Fallout 3 mods and community
Needed for a lot of mods that use additional scripting. I think FOOK2 needs this. Good to have either way.
There are A LOT of other mods, but the above are the absolute best for making FO3 far more immersive, balanced and kick ass. You shouldn't have any issues installing the mods, but if you pick some up and need help with load orders and what not, let me know.