Civ 4

http://www.strategyinformer.com/pc/civilizationiv/review.html

That's a good rundown of some of the main changes... but...
Ok, there's this civics thing, that can give you different ways to handle your government. Slavery, Caste system, etc. It's 5 catagories, each with 5 options (the base, no bonus, and 4 different bonuses depending on which you use). The options open up as you develop techs.

Religion is still kinda growing on me. I don't have a handle on it yet.

Resources (gold, stone, etc) are only active when you improve them.
There's a new improvement cottage, which upgrades to hamelt, then something else, etc... which adds a $ token to the square. Roads don't seem to do that anymore. I need to verify first though.

Everything you need to understand your city and it's updates is visible from the main screen, you don't need to go in to city view to see how things are going, and which squares are being worked is shown there on the main screen through subtle animations. It sounds hard to follow, but quickly in you get the hang of it.

Being a pacifist doesn't get you out of maintaining an army. The enemy thinks you're weak and has a grudge, BAM war. Deal with it hippie.

But that's not to say you can't have a peacful game, it just takes more work than it did before.

Back to land improvements... just because you have a city with good production doesn't mean that's the best place to build your wonder. Wonders seem to get bonuses if you have a resource being worked in the city. IE Stonehenge had a +20% bonus to be built if stone was in the area. I remember seing one for Marble as well.

Units and advancement. I don't see a defense rating for units yet. I may be missing it but it's possible it's not there. I do see a little flexed arm with a number, and a couple feet with a number. One is obviously strength and the other movement. The HP remaining for the unit are shown by how many little guys are standing there.

Ok, advancement. When your unit gets promoted it's not just a flat improvement, "I'm a spearman but better", kinda thing. Instead you get to pick HOW they improve. Maybe you want to make your swordsman city raiders, so they get a +20% when attacking a city. Now you'll probalby want to assign that spearman a +20% against melee attackers to defend your city. So it won't be ideal to raid the enemy, but it will hold your city better. So even troops have more strategy to them.

Settelers and workers no longer lower your city size, instead, you just take a growth hit while you produce them.

Graphically it's a big step up from 3, but it still maintains that grid style game play. So it feels familiar, but you know you've got a lot to learn before you're good at it.

So, here we have a very strong contender for game of the year.