I rather hate the massively favored defensive bonuses anyway. I could do without fortification at all. Civ IVs power system vs how easy it is to take cities is out of whack ----> part of the reason the AI sucks so greatly at war. It considers garrison troops in its city that are coded to never move as "power" and only takes a marginal consideration about walls/positioning etc.
However, attacking it on most speeds is annoying as hell due to the massive

bonuses and the super duper uber defenses that allow one unit to kill 3 unless you do something about them. That's all well and good, but what really irks me is a civ doubling up its already substantial army mid-war, or teching out 2 techs AND having the money to instantly upgrade every defender it has. If you want realism, this fails. If you want balanced gameplay, this fails. It fails no matter what.
So while I was sarcastic about how it randomly takes years to get even a 5% fortify, allow me to be completely serious:
Troop movement vs tech pace vs troop production is completely ridiculous in this game. It's why I repeatedly have said that I WANT to play quick, but that the speed was thrown in as lip service and little else...it SUCKS. IMO even normal is pretty iffy. It just doesn't sit right that longbow civs with 10 cities can get 2-3 techs AND rifles in the middle of a 20 turn war where they do nothing but spam units. Can I work around it? Sure. It still bothers me a lot though.
IMO it should cut both ways too. Players get away with too much at war because of how the AI looks at power. IMO either nerf defenders, make units MOVE AT DIFFERENT RATES AT DIFFERENT SPEEDS, or adjust the hammer/upgrade costs to make war more palatable.