Civ3 improves on Civ2 in many ways. There are a few things missing but for the most part, Civ3 is far superior. Here are some annoyances from Civ2 that were fixed in Civ3.
- "8 units destroyed", i.e. stack death. Unrealistic and unbalancing. Civ3 allows you to concentrate your forces without such huge risk. The first time you see an AI SOD (stack of death) heading into your territory, you'll wake up to the age-old strategy of concentrated power.
- Too predictable combat. Let's face it, we all knew that Rifleman on a mountain would always, always beat Cavalry. Fewer hps in Civ3 means you have to plan your offense and defense for contingency. More importantly, combat uncertainty in Civ3 leads to needing to use combined arms (defensive units, offensive infantry, fast movers, artillery). No more "killer units" like Cavalry or Howitzers.
- ZOC. Why should Warriors stop my Tanks from moving right by them? Combined with predictable combat you could basically just build a couple forts, plop 1 or 2 units in them and guard an entire continent in Civ2. Worse, the AI would continue to bash its units into your fortified positions over and over again. ZOC no longer prevents movement in Civ3 so you better pay attention to protecting your land.
- Spies and Diplos. 30 units that can almost singlehandedly conquer or bribe the world. Way way overpowered plus the poor AI never had a clue on how to use them. Civ3 does away with these cheats.
- Caravan hoarding for wonder building. Another human-only exploit. Except for the very occasional great leader in Civ3, there are no shortcuts to wonder building.
- Steam Rolling, i.e. once you are "on a roll" you can quickly use all those conquered cities to add to the juggernaut until soon it becomes unstoppable. Civ3 puts the brakes on steam rolling: Conquered cities have resistors and may flip back culturally. The corruption model no longer allows an infinite number of productive cities. You can't use roads and rails in enemy territory. No more gaining a tech every time you take a city.
- Michaelangelo's Chapel, Leonardo's Workshop, Adam Smith's, Statue of Liberty. All overpowered wonders now signficantly toned down in Civ3.
- The Bomber cheat. In Civ2, Bombers could protect all units underneath them from attack, except for attack by fighters. And with ZOC, you couldn't even move around them! Mostly this was yet another human-only exploit.
- Uneven diplomacy. There wasn't much you could do in the Civ2 diplomacy screens. Civ3 opens up a whole new world in this area.
- Fundamentalism. Gone in Civ3. May it RIP.
And these are just the things fixed from Civ2 to Civ3. Civ3 adds even more to the game: trading, culture, resources, new victory conditions, more govenments, meaningful civilization traits - and more of them, Unique units for individual civs, the Golden Age, and more configurability of more game parameters. As a long time Civ2 player, Civ3 to me is a greatly superior game.