This review may be coming too late... but just because I have been comparing this game carefully to make up my mind
Still it has its flows, so here are the main points between SupCom and SupCom2
+ Tech Tree is funnier and better than SupCom 1
++ The factions are far more different from each other than in the former game, Seriously this is essential!
++ The game speed (honestly!) is heavenly better than SupCom 1, I know strategy shouldn't be fast as we are used to, but SupCom1 is simply hell slow
+ The mix of units is funnier as well as the different strategies you may take
+ Some elements are easier/better to implement, like using shields and so on
++ Far more experimental units also
++ Still, is NOT A CLICKING GAME, COOL!!!
+ Campaign has also been too criticized, the story is weak but I find the campaign battles fine
-- The greatest issue, I can't figure why the hell they removed the extraordinary economic-build-support system of SupCom1
- No huge maps
- Removal of certain strategy elements like cloaked and stealthed units, these should have been improved, not removed
-- The importance of navy has been seriously diminished, not to say that even doesn't exist a decent skirmish island scenario
- No map editor
All in all after the comparison may seem that SupCom1 is better than SupCom2, but by experience I personally enjoy more the new game, among other things because of the game speed and the different strategies you can follow, I loved also the Cybran Navy (now the whole navy can become amphibious). What is great about this game, unlike others is that there is not a single answer, from medium, long range artillery, shields, nukes, navy, experimental units, ground and air forces or a mix of all these, this game offers great possibilities if you really love strategy.
I want to believe that one day we are gonna get a SupCom3 with the best of the 2 worlds.
Note about Starcraft 2... sorry guys, but I honestly think that SC2 sucks, all you have is the old formula, I didn't like the new mix of units and if this game is cool somehow, is just because it is based on its predecessor. But again, no WMDs? no Medium - Long range units, artillery? Even the tanks became weaker (shorter range) and hell useful units like hydralisks became totally meaningless and if a unit is meaningless shouldn't be there in first place, right? I know this is not SC2 review, but I'm making a point here for comparison, in SupCom2 you have a lot of things that SC2 may wish to have.
Still I'm surprised about SC2 success, but not that much, marketing is a hell powerful tool!