gyokzoli: The difference is huge. You have to learn the game from the basics.
Turns out that my brother had it so I actually played a game - yep there went my revision day. To be honest, I really liked it but I don't think it was as polished as Civ III. Oh and by the way, I played with the unofficial patch that came out last year, and I played Crossfire. And I would disagree with your statement, I believe that it's pretty much Civ 3.3 or so.
The unit upgrading thing is pretty much akin to Civ IV in the sense that your units can go in different directions. Yeah it's quite cool, but I felt that in the end it was quite arbitrary? Sure I played on the easiest because I wanted to have a quick playthrough, but I just don't think I could be bothered to constantly customise every single unit? The workers are enough (though I did have them automated this game since I'm not fully aware of the worker mechanics). Anyway, it's not a biggie since you can streamline it fairly quickly, and you had unit upgrading in Civ III anyway.
I somewhat like the new research thing because there are less gaps as a result, i.e. in Civ III the difference between Knights -> Cavalry (4->6) is just such so huge and that's how you time your attacks, also taking into account that Knights were an optional technology. The marginal upgrades lead to a more balanced game, but also make it more difficult to capitalise on your edge.
I liked the improved policy and diplomacy tabs, though I had a very difficult time getting out of wars and spent the entire later half of the game at war. It was ok, since I was playing on easy so I could hold them off with minimal forces but I just wanted to tech in the end and see how it ends up like. Basically, every time I would make peace with someone, another faction would declare war on me as a result of that, which made it basically impossible to get out of wars towards the end. I even ended up bribing them, or taking some of their cities, but they would still immediately declare war on me even after having accepted the reparations. Pretty annoying. Oh and then another one would simply just declare war on me because he was a commie bastard and didn't like my wealth building nation.
The politics, economy etc tradeoffs were quite cool, but it's ultimately the same in Civ III, just a little less customisable.
So sure this diplomacy based politics thing seems like a nifty idea but I don't think it worked out as well as it could have.
The building trees were pretty much the same, equivalent to the Library -> University -> Research Lab tree, and equivalents, as in Civ III.
Population management was virtually identical to Civ III, i.e. need Aqueduct, Hospital to grow beyond a certain number. Need to balance happiness (psyche) with research, taking into account the unhappy citizens (drones) and happy citizens (talent) balance, using entertainers (whatever they were called), etc, etc. Virtually the same.
City management with tiles was virtually the same as well.
As far as the different civilisations go, I'd say it's not different from Civ III. Depending on who you pick, you will have a hugely different game, even more than in SMAX I believe, since it's possible to marginalise bonuses quite decently in this game it seems.
So to the pros:
I quite liked that there was a storyline in the back of all the things and it was also refreshing to only play in the future, which I felt was something that Civ III somewhat lacked at.
I liked the random alien invasions etc, those were quite cool, since Barbarians became obsolete very early on in Civ III.
Building in the sea is also cool, very nifty idea indeed and the Pirates "race" must lead to quite a varied gameplay.
Cons:
The "advisor" overview things I found extremely unsatisfactory and lacking.
There was no single screen that showed for example, my shield production (whatever the equivalent was in SMAX). I simply had to cycle through my cities on by one to see how well they produced. Yes, it shows how far done they were with a particular project, but it didn't show production per turn. Is it possible to turn that on somehow?
Territory and picking a place where to build a city were cryptic as well, would have been much better if it showed simply clear values with numbers besides them.
Upgrading was a bitch due to (even under the F4) tab having to individually click every single unit to activate it, in order to repair it, which if course meant that you had to fortify it again the following round. Units didn't show above cities but I'm pretty sure you can turn that on somewhere.
I felt that some of the concepts weren't explained quite as well, i.e. like Planet Status, or whatever it was called. How do I see my value for that? Nothing on it in the databank. Also, my workers didn't tell me why they were discontent? War weariness? Is that even a mechanic in the game? Overcrowding? Oppression?
Overall, the game is conceptually very very similar to Civ 3 with mainly arbitrary differences, which I find a shame. I really enjoyed playing it but I very much missed a proper overview tab that would have enabled me to have more control over my "empire".