A stellar update to SupCom, but not without it's issues.
So, let's first off cover all that has been improved. Obviously we have lots of new units including an entirely new faction. Lots of the units are very nice additions. In fact I'd say they are all very welcome changes, being both useful and not overpowered. The new race, the Seraphim, can seem like an original SupCom race if you look at their available unit list, which is quite a bit more trim than the current other races, but many are mutli-function units, and they seem to balance quite well.
Beyond the new units, all the old units have been looked at. Some have been tweaked, others completely overhauled, and the new version are almost universally better. Despite what GS claims, Nuke launchers didn't receive a nerf, but actually a buff, just one that comes at the cost of being able to assist either the nuke or the defense buildings in any serious way. The experimentals in particular have been heavily tweaked in many cases. For instance the Czar, which was practically useless in my mind, has been given a major buff for the most part making it a very good unit now.
Graphics have also been given an overhaul. The default ui has been swapped out, and the new one is a bit better than the old one. You can now zoom in even closer, and texture details have been improved as well.
And lastly, the AI has been seriously looked at, and is a very much improved. The old AI was quite laughable for any experienced player, but the new one can quite dangerous even on it's lowest setting (although the turtle is still pretty bad).
Now, all that said, there are issues. First of all is performance. The old one I could run at highest settings on all but the biggest maps. However, the new one is giving me odd sound issues even on fairly small maps. That said, it is likely due to running at top settings, so it expected. The demands placed by multiple AIs is also rather high, and can bring my system to it's knees, but I think that is actually because the AI is actually doing something this time around with usually several hundred units, where before it was quite dormant most the time.
Probably the biggest issue I have with the game is the single player campaign. It's pretty good for 1 time playthrough, but because all the factions use the same campaign for the most part, it seems rather weak. Additionally, all the maps are easily conquered with the same 'dig in and exploit the first objective's lack of time pressure'. The campaign certainly could have used more thought.
My last gripe with the game is the new UI. While overall a better UI, some choices they made seem silly and actually made aspects worse. For instance, you no longer see your entire build possibilities when selecting a builder, instead you have to scroll left and right. Also, if you select builders, you don't get to see any count of the number you have selected, instead you only see their potential build orders. Lastly, for upgradeable buildings, it is difficult to tell if the button you see if the buildings type, or the next upgrade.
In conclusion, for any sup com owner, Forged Alliance is a good purchase. While the campaign is weak, most real players will be having their fun online or in AI skirmishs and here FA shines as a massive improvement.