I agree, and that is so sad. Why? Because the modern age has the potential to be the most intriguing. I think there are a few core reasons behind this boredom:
1) In the modern age, you are pretty much just down to a few key units, with few-if any-promotions that are useful anymore.
2) Pretty much everyone is running nearly identical civics, and religion no longer has a role in relations whatsoever.
3) As was stated above. If you are winning by the end of the renaissance, you will probably win the game outright.
4) The map is completely discovered.
5) Great people have much less impact on the game, and YES the Wonders are few and far between.
So, how do we solve these problems? I have made these suggestions before, so please forgive me repeating them (albiet in brief).
1) More is not necessarily better, so I wouldn't say 'give us more units'. Instead, I would say give us more modern-age specific promotions, especially for naval and air units (oh, and spies of course).
2) Revamp Espionage to make it more interesting, and allow for a multitude of non-combat conflict to be resolved in the game (Cultural and Economic Warfare for example).
3) Bring in Ideology alongside the existing Religion system-and along the same lines (i.e. found an ideology and try and spread it throughout the world).
4) Limit early unit movement so that more of the world is unexplored in the latter part of the game.
5) Take barbarian nations that extra step, and make them fully-fledged Minor States, with whom you can negotiate and/or wage war (especially useful with the Warlords Vassalage system!)
6) Implement a system to reflect the ups and downs of civilizations, so that mismanagement or dirty tricks can bring even a winning civ to its knees.
Anyway, those are just a few thoughts. Maybe a future expansion will see Civ4 be the version that finally does away with Modern Age Malaise for good.
Aussie_Lurker.