My biggest gripes with Civilization IV.
- It's buggy. Buggy as hell. It's also somewhat of a memory hog. It can run perfectly well on a minimum specs, or maybe not - the problems do not seem to be really consistent and the game also has a nice memory leak, one of the biggest I've ever seen on this hi-end game. Epic/large endgames cause stutter, freezes and crashes even on most high-end configurations. Right now the game can really be unplayable and it's more a question of luck than of hardware - caveat emptor, basically. The updates, especially one fixing the memory leak and CG leader heads, are on their way but pretty much essential.
Aside from that..
Bombardment was much better in CivIII. Now you basically have to suicide rush a city with your catapults/cannons/artillery (yes, no more mobile dedicated artillery

) to wreak havoc. Destroying improvements and directly attacking enemy forces via bombardment requires aircrafts - battleship cannot bombard terrain tiles, or at least not so on first two levels unless I am completely ****ed up. Also it will by default cause more or less no collateral damage. The result? Three BBs floating on an enemy coast usually just manage to drop the city's defence modifier to 0% and not much else. To actually **** **** up you need an army of carriers (one carrier can also carry just 3 fighters/jet fighters).
For some ****ed up reason it's not possible to intercept enemy air units over their own city, so modern war against an enemy with even a minor airforce becomes unrealistic slaughter. Minor issue? Definately not so in modern times. Gandhi is still not a pacifist and Aztecs are the most damn annoying neighbours you can get. Gunships seem too fragile. Carriers are still too cheap (cheaper to produce than one battleship, actually). Cost of updating an unit is so high that it's easier to build completely new units than to update to newer configuration (it can be something like 300GPs for updating a knight to cavalry. Just one knight, mind you.)
Defence/offence ratings for units are, however, much better - spearmen are no longer the invincible arm of God which can destroy modern tanks with ease. (Actually, even basic infantry has real problems beating modern armour with city raiding updates.)
The CivIII "health+combat bonus" is scrapped and replaced with dedicated updates, promotions. You can promote your cavalry as more mobile, just stronger, more efficient against infantry, medics and so on. With right civics - which are absolutely fantastic - you can make pretty dedicated units and stacks prior to rough combat.
Personally I still enjoy the game a lot and give it 90 points, but bugs, resource-hungriness and aforementioned minor issues (mostly making warwaging more difficult) drop the rating.