A few basic observations (from the limits of my four full playings of the game).
I managed to play 4 full games in under a week. By that I mean I enjoyed 4 games in under a week. I usually get exhausted from a playing of Civ IV and then don't touch it again for often a month or so.
I routinely get to see the entire map on Warlord level. Good luck seeing the entire map in Civ IV even if you are kicking major butt in Civ IV.
In Civ Rev, naval is worth having, in fact if you ignore it you likely ain't going to win.
In Civ IV I usually consider naval worthless until you can build modern naval units. And by then I have usually already won, the naval is just for being a bully.
In Civ Rev all your time is spent playing.
In Civ IV all your time is spent micromanaging.
Decide what you consider important I guess.
In Civ Rev you rarely send units on tours of exploration that seem hopelessly out of sync with reality.
In Civ IV, it seems ordinary to send a unit out mapping and they might neeeeeeever see their homeland again

They leave as club wielding warriors of the tribe, and when they get home, everything they ever knew is gone
In Civ Rev the military upgrades are actually useful sounding.
I have also found that in Civ Rev 3 units are as effective as 30 in Civ IV. The point being, you chase around a lot fewer units.
I have also noticed in Civ Rev you can't just look at enemy units and know everything about them. Nice fog of war aspect there.
There doesn't appear to be much in the way of animations in the DS version. So what, they would only eat hardware resources.
The much mentioned in the past "how did that archer kill my friggin tank unit" has not gone away. Deal with it.
It doesn't kill the game any more than it ever did. You just don't send one tank unit into a swarm of low tech anything.
Mobs kill.
Techs are totally redone. It's a new tech tree, much the same look, but don't expect a carbon copy replay of Civ IV.
The Wonders are about the same. They do a lot of the same old thing, but not a carbon copy at all. And as always, you want them for the perks.
In the new Civ Rev, the guy that gets the tech first usually gets a neat freebie unit. Being the only Civ with a critical military unit can be quite impressive. Speed is everything, having it for 5 turns before anyone can adapt means a lot actually.
Government types are important, but Sid booted the whole religion thing from Civ IV out of Civ Rev. Civ Rev is again all about the best tech and the best army.
Great people, these guys are cool. You get them likely sort of as fast as in Civ IV (seems that way). But what is fun, is a spy unit can actually kidnap them

Did that once. And then you put them in one of your cities and get their effect for yourself. Spy units though seem to get caught fairly often. Well I lost 2 out of the 3 I have used so far at least. They don't seem all that invisible.
I've missed the Great Generals of Civ IV though. Well it appears they didn't make it to Civ Rev.
In combat, it appears you MUST have supporting units. In the early game naval support and archer units look like key items to ensure you have. Naval support is auto engaged, you just need to be adjacent to your ground unit that is attacked. I've won some battles I am sure I would have lost without that naval support fire. Late game bombers rule.
It also seems that the person with the best navy is hard to beat. If you have galleys and they have galleons you got nothing. And the person with cruisers won't impress the person with battleships.
City building. It appears making settlers reduces the size of the city that made it. But there is nothing wrong with more and more and more cities. Make em as much and as fast as possible. But make sure you make them produce culture fast.
And walls, you WILL make walls in your cities.
Walls keep them from converting to the rival. And your cities will quit you the second your rival's culture looks better. I played one game where I stole almost half of the cities I ended the game with. It's not hard to do either, so expect it to not be hard to happen to you.
Strictly software speaking.
I am not happy there is no form of zoom, but it's not like the map is really large so it's not the end of the world.
The interface is very easy to use, and learning to run the game is very basic too. Manual is not really required.
The tutorial is part of the actual game. Each time you do a new "thing" in the game, you get an adviser that tells you about it. Each time the adviser also allows you to turn off the adviser function.
The combat animations are basic, and handy. In Civ Rev, if it "looks" like you will lose, you can hit the panic button and run away to fight another day. But you are punished for cowardice, the victor gets 3 upgrade credits instead of one.]
The game allows several saves, but, it appears the game doesn't keep much of a memory of past gaming.
They offer a "game of the week" option, but it doesn't look there is any way of accumulating these beyond the current playing. All you can do is find a way to port the roms data elsewhere and that is NOT my idea of a solution.
With Age of Wonders: Age of Kings, the more you played, the more valuable defacto speaking your specific game rom became. Mine is sure worth something to me.
I had a Steel Horizon rom die on me right near the beginning, and I was NOT happy needing to re acquire all that I had lost.
I've seen Civ Rev played on my friends PS3 and it looks apparently no different (other than a big screen HD experience is graphically much more amusing).
Ok that is I think the limit of my observations to date.
I have seen much buzz about many rpg DS titles. I am unsure how many will enjoy a classic turn user strategy title. But I DID uninstall Civ IV today. I DO like the DS game that much.
No I am not going to play it all day for an entire month though

I might average a few games a week for the first month or so. But, if Panzer Tactics wasn't safe just because it has tanks, I think it would have lost first place with me.