I use mods to make F3 look better, make the game more challenging with the focus on roleplaying, realism and immersion, and to add new things to the game for me to use, discover and explore. Check the 'Fallout 3 LP' playlist out if you want to see these mods in action as I roleplay through F3. This is also the mod setup I'm using on my Let's Play Fallout 3 on YouTube. Here's a list of Fallout 3 mods I'm using at the moment.