you know i tried playing civ 2 today, and the attack/defense system just seemed so gimicky and stupid to me now that i'm used to civ 4 combat. For one thing, it means that the best way to defend a city is with attack units like catapults and cannons, because they can just own anything that gets near the city. You also get stand-off situations, where two cannons are 1 square apart, and whichever one moves next to the other will be destroyed, just because it's defending. That's incredibly lame. And of course the stupid civ 2 AI falls for it every time...
I remember booting up a mod I found here for Civ2, and thinking exactly that.
As it was mentioned above, having separate (and wildly different) attack and defense values makes zero sense for a unit out in the open. If you have two 4/1 units facing each other, each on grassland tiles with no funny business like rivers or fortification, why does the attacking unit get such a huge advantage? It's not like every single time you launch the attack, your opponent's troops are sitting in their camps drunk and scratching their nuts. And vice-versa. It's not like a piece of terrain in Civ (not including mods) represents a few square miles and you are maneuvering your troops for a specific assault on a weak point. Each tile in Civ represents a huge swath of land, hundreds of square kilometers, where a campaign is fought out over the course of a year or so, and then you get the results afterwards.
For example, say I have a Standard-sized map of the World. Earth has a surface area of roughly 510,072,000 sq. km. If I use most of the map generator info from here:
http://www.civfanatics.com/civ4/reference/map_scripts_guide.php, then I have roughly 84 x 52 = 4,368 tiles. That means each tile represents ~116,800 sq. km. (!) Even a double-sized map, with 168 x 104 = 17,472 tiles, each tile still represents ~29,200 sq. km. Why should my unit get a massive advantage for attacking your unit in that tile? What special factor makes my moving into that tile so unique as to warrant an additional bonus or penalty?
Having a base strength with special terrain modifiers and the like (like archers getting a bonus in cities or on hills) makes the most sense to me because it reflects a reasonable baseline (troops equipped with melee weapons have these characteristics, troops with guns have these, mounted have those, etc.) while giving you a chance to customize each unit. Can you still customize with A/D type units? Sure, but the reasoning above is why I think the base strength approach is better.