Better game pacing is reached by reducing XP rewards for combat, lockpicking and hacking, thus focusing the big XP gains on doing quests. I felt that fallout3, especially on the high difficulty settings, punishes you for exploring by upping your level way too fast. consequently you could only see about 1/10th of the game before hitting the level cap and having only top-of-the-line enemies and gameplay that stops developping. Now this takes a lot longer, and you get to explore more and be introduced to better items and enemies at a better pace that matches the size of the game.
Version 1.0. For best results start a new game, but it's completely save-game compatible.