Yes, the combat system can be annoying, such as Musketmen sometimes losing out to Swordsmen but it does mean a single tech advantage gives a nation an edge but not practical invulnerabiity. As in real wars, the direction of battle can change frequently and a tactician has to take this into account.

I like the trading system, including strategic resources such as Iron or Oil, though such resources ought to have a concurrent usage limit. The key to the game is diplomacy! The AIs are sharks. Trade hard, trade often and keep your swords polished. Keep an eye on the Trade Embargos and Mutual Protection Pacts between rivals. Make sure you have friends, especially for those important strategic and luxury resources.

Warfare is now more challenging. The AI no longer attacks piecemeal. Attacking units come in mobs and your sword had better not be dull.