I recently got Supreme Commander and have proven, several times, that despite meeting the minimum requires, my computer really can't play the game. (Among other things, it's crashed half the time I've tried to play it, and one of the only games that didn't crash fell to below 1 FPS when I was attacking the enemies main base.)

So, since I can't actually play the game, I can't exactly create a review for it. Instead, I'm going to compare it to Total Annihilation, since Supreme Commander is TA's "spiritual successor."

First off, unit types. TA had four unit types: KBots, vehicles (tanks), airplanes, and ships. (This was later expanded to include hovercraft.) SC simplifies this to three: land, air, and water. While there are no units called kbots, all three factions have large walking robots (excluding the Commander, of course). So there's a smaller collection of units to contend with, and most units take on roles similar to TA: anti-air, anti-land, anti-water, anti-base, and others.

The main difference unit-wise between TA and SC is that in TA, each unit type had an associated Construction craft. SC eliminates multiple construction types: there's a single amphibious Engineer unit instead, and all unit factories can create it.

Next, tech levels. TA had two tech levels, while SC has three (plus a fourth experimental level, more on that later). In TA, higher tech levels were reached by building Tech 2 unit factories, using the appropriate Tech 1 Construction craft. (So to create Tech 2 ships, a Tech 1 Construction ship had to be created first.) In SC, however, all unit factories start at Tech 1 and have to be upgraded to the higher tech levels.

In TA, Tech 2 Construction craft could not create Tech 1 buildings (with the exception of their Tech 1 unit factory). In SC, on the other hand, an Engineer can produce any unit up to their tech level. So a Tech 2 Engineer can produce Tech 1 and Tech 2 buildings, but not Tech 3 buildings. Tech 3 Engineers can also build the experimental units, which are constructed like buildings.

In TA, your commander could only build a subset of Tech 1 buildings. This remains true in SC, however the commander can be upgraded to higher tech levels. Once upgraded, the commander can build at the level of the given Engineer at the same tech level. So a commander with the Tech 2 Engineering Package upgrade can build all Tech 1 buildings, despite being originally limited to only a subset.

Resource management in SC is almost identical to resource management in TA with a few notable exceptions (beyond Metal now being called Mass).

The biggest change is that Mass Extractors can only be placed on Mass Extraction points, while in TA Metal Extractors could be built anywhere (but were only really effective on metal points). This seems to suggest that there will be no metal maps - but I can always hope...

The other change is that Mass Extractors can be upgraded, as opposed to TA, where they had to be manually removed and replaced. While upgrading, they cease their mass output, though.

Overall, Supreme Commander appears to be, if anything, better than Total Annihilation, which is really just about the highest praise any RTS can hope to get.