Well, the demo was a bit neutered when it came to long-term stuff like vehicle design (it wasn't available)... besides, you have only 90 minutes of demo time, not enough to really do anything that time-intensive anyway.
Combat - strategic weapons were disabled (probably the only time the SP franchise has never gone nuclear). conventional combat is handled similar to A&A where various units line up against each other and combat is somewhat abstacted. Instead of the topo map and having to hunt for the bad guys, you line up on one side, they line up on the other, and you pick your combat style (full assault, defensive, stand off, etc.) and the units 'line up' on the upper half of the screen not unlike the old A&A board game. The lower half has a 50/50 green/brown map representation that you can see your unit types (tanks, infantry, attack helicopters, fightes, etc.) moving across as white dots. Depending on your strategy, certain units will advance, hold their ground, or fall back (if you pick air supremacy, your fighters go forward and your ground units hold back, full assault, all move forward, etc.). The 'winner' slowly has the lower map slowly turn their color, like a percentage bar until they win, while the upper 'battle representation' has 'units' enage each other by some formula and the numbers just start dropping for each 'hit'. Very abstract; you pick the strategy (which can be changed mid-battle) and the 'units' do their thing.
I didn't like the movement on the strat-map much. It seems units in the same country will not auto-engage and you can have multiple fights occurring in the same territory at the same time (the demo scenario has you as Russia regaining her lost glory by taking the Baltics, Ukraine, and Moldova back... by force is necessary (required more like it!) in 90 minutes or (in my cases), roughly 5 years time.
There is also a covert ops section where you 'deploy' cells to other countries and pick missions for them ranging from sabotage to assasination to general terrorism, you can pick the severity, and if you want, a country to blame (didn't work too well when I went after Ukraine and trie to blame the Romanians).
foreign relations - I didn't really get too much into this (the demo scenario has specific goals that don't use this very much). It allows a multitude of treaty types (foreign aid, economic, scientific, trade, military, defense, coalition, etc.). The only gripe I had is that the pull-down country list always started at 'A' and you had to scroll down to find your country; no way to just pick them off the map. There have been lots of improvements and option added here for more 'real world' choices.
Economics - massive changes/improvements. No more simple sliders with a limited number of 'resources'. Now, you have a giant list of 'products'/'resources', a world market, foreign trade levels, investments, and such. Again, the small 90-minute timed demo didn't allow me a lot of time to play with this, but you can see what areas you import and export and make adjustments to your investment, tariff, and export levels.
budget - lots of categories this time, but you really need some more instructions on what each does (yes, generically they're self explanatory - infrastructure, tele-com, heath services, police, etc.) but beyond that, I couldn't really tell what each one did (not that I could 'afford' to keep any in the green anyway). Of course you have the usual tax adjustments (corp and private) as well as controlling the national interest rate (I think that's what it was).
government - you can change your government style from multi-party democracy, to single-party, to communism, to dictatorship, etc. which of course affects the stability of your country and your popularity (I imagine it effects much more, but I couldn't see the effects).
main map - there's the standard geographic map with at least a dozen overlays like political relations, government support/approval, tech level, military might, etc.... lots of color scales to show this info.
It definitely has more going for it than the original, especially in the foreign and economic areas (though it's hard to see much in only 90 minutes). The combat has been simplified (maybe too much for some) given all you do is line up, chose a strategy, and watch your unit counters tick down.
I'd wait for PCG and other's reviews myself before making the buy/no buy decision. There just wasn't enough demo (options and time) for me to explore everything enough to gve it a thumbs up or down, just that there's a lot more here than the original had, and it seems to be more good stuff with more options.