I know the feeling. I finished one game, then started on the second one, but couldn't find interest to finish it. Then I played RTW again for a month or two, until I thought "let's Civ4 another shot!" I played a game at monarch level, lost, prince level, lost as well
, now at noble again, and am winning, barely. I'll try prince next time again and do find it fun again and challenging to search for the possibility to win!
Think about this: there are a lot of experienced Civ-players who have beta tested and still play the game thoroughly, trying to get the highest score possible. Who do find Civ4 fun, game after game. And I thought I'd seen it after one game, but 'refound' it. Perhaps you should give it another try as well.
(Unless you want to perform optimally at school/work.
)