OK, this game is amazing.
It may not be a complete gamechanger, and it's similar enough for Civ veterans to jump right in, but... oh my does it make me feel like a total newb.
The sheer amount of different techs and tile improvements is staggering. In addition to the number, there are techs that modify the tile improvements.
The trade route limit being per city instead of for the whole civ makes quite a bit of change too. No longer is there the I-WIN button of Civ of picking Tradition first and stopping expansion at 4 cities - in this game you'll be expanding until the very end of the game to become stronger.
The orbital layer is an interesting addition - aside from the miasma-removing satellites, you have ones that improve tile yield (one for each type - energy, production, culture, food), tactical enhancers for your units, combat satellites that can bombard the ground, science-enhancing ones... their areas of operation can't overlap so some planning is needed.
Managing health (which is the new stand-in for happiness) is different this time, too - no more are there any luxury resources, all the health benefits you get will be from buildings and virtues. This adds up to the general theme of this game to emphasize strategic resources more - you'll want all the firaxite/biomass/floatstone and all the petroleum, titanium and geothermal energy you can get your filthy man hands on. You'll never feel an overabundance of resources, which is just perfect. Do note that not just your affinity's special units require your special resource [and not just 1 per, the Supremacy special artillery takes up 4, and their ultimate unit - the awesome Angel - takes 10 (!) ], even if you don't go all military on the planet's ass, special buildings also require a hefty amount. Between your special stuff and satellites, you'll be wanting those tasty resources a lot.
Affinities are... great, though I must say Purity units look pretty damn boring (except the tactical suit unit, these look like cyber-roman legionaires

). Getting affinity points is what will more or less guide your research about half the time, as you'll need to keep up in your chosen affinity or get destroyed. All unit upgrades in this game come from affinity levels, and the differences between levels are quite big. A faction 3-4 affinty levels behind can at least cause some trouble for the attacker, but more than that is a total steamroll (cities don't seem to fall too far behind though, with plenty of +combat buildings).
Then there's the tech web. I like this new model. There's no way you can just monopolize all wonder production due to getting to all techs before the other factions. You'll pretty much never be able to research everything in one game, so you prioritize a lot - this also shapes gameplay for the three affinities differently due to available buildings, wonders and tile improvements. There's a considerable amount of freedom to this system.
Then we have the trade. With a trade depot and if you pick the right option for Autoplant buildings, you can have 3 trade routes per city. You have your internal routes that boost both cities' food and/or production yield, and international trade routes which provide energy and science for both parties. There's also stations in the game - the 'new' city states - which have unique combinations of trade yields and level up with each completed route. These tend to hog valuable land, though, so you'll see them dropping like flies, and likely destroy a few yourself.
For espionage, there's your standard city infiltration, though there's more option than in Civ. You can steal energy, science points, technologies, make units defect, hack satellite coverage, even use a massive attack or stage a coup. I'm not exactly sure how Intrigue levels (0-5, determines which missions are available) work so I've not a whole lot to say about this system. One more thing is HQ projects - if you don't want to go spying much or don't feel like you need all your agents for counter-espionage, you can keep them in the HQ for a small bonus for each (like extra health, production towards wonders etc). Neat.
So then there's diplomacy. I must say I've played a selfish asshole these 3 games I've completed so I didn't have much of a look at the whole Favour system just yet. Enough to say for now, though, that various stuff affects your relations - trade routes, affinity, how you treat the aliens, if you've been doing excavation near them, border friction, warmongering, covert ops... not extremely complicated but it's still better than Total War diplomacy.
Last but not least, the aliens. I think they did them right. At the start you're pretty much huddling around your city trying to not make any bugs mad as they're stronger than your starting units and there's a lot of them. You gradually become stronger and can overwhelm previously overbearing odds, turning the tables on the aliens as the game goes on. I'm not sure if that global aggression level is working or not - seems to be, in any case - but I like them a lot more than the barbarians of civ.
So, first impressions - here they are. I'm probably going to spend a lot more time on this in the coming days.
It is not the critic who counts; not the man who points out how the strong man stumbles, or where the doer of deeds could have done them better. The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood, who strives valiantly; who errs and comes short again and again; because there is not effort without error and shortcomings; but who does actually strive to do the deed; who knows the great enthusiasm, the great devotion, who spends himself in a worthy cause, who at the best knows in the end the triumph of high achievement and who at the worst, if he fails, at least he fails while daring greatly. So that his place shall never be with those cold and timid souls who know neither victory nor defeat.