Way back in the day, in the early days of real time strategy game development, there were two games that came out at roughly the same time: Total Annihilation, and Starcraft. This was a crazy time, when PC games were still king, World of Warcraft was barely even conceived of yet, and cellphones were barely capable of making calls, let alone playing full versions of Final Fantasy or Sim City.
If you haven't played either of these, you're probably too young to remember (damn you young kids) or older, in which case you probably won't give a crap. The two games had some rather profound differences. There were other RTS games out, but they were all pretty shitty. Starcraft and T.A. were pretty much the best ones out there, with Warcraft 2 still getting plenty of play.
Starcraft, which later became the unofficial national sport of South Korea, was a sort of representational game, much simpler in interaction but with far more character development and faction differences. T.A. was aiming to be a lot more big-picture tactical and to have a hell of a lot more options and strategies. Starcraft, by comparison, felt a little childish and simplistic.
Now, keep in mind, that was just my impression at the time. I really wasn't that keen on starcraft, even though I played the hell out of it. I just liked the full on battle feel of T.A. better, even though the game had some fatal flaws with its AI engine once a lot of units started crawling around. Of course, if you look at the sales and continued popularity of Starcraft, and the collapse of Cavedog (the company that put out T.A.), it's obvious which game stood the test of time. There was even a high-fantasy T.A. called Total Annihilation: Kingdoms, which was a bit of a flop, as far as I can tell. Not a bad game, but it was lacking in the charm and character that Blizzard does such a good job of putting inot their games.
I think what it was is that T.A. was an RTS game designed for brainy nerds who over analyze everything. Starcraft was, well, built for a broader mass appeal. Starcraft also had some of the best balanced units across three very different factions I've ever seen.
So anyway, moving on, it's 2010, and there are now successors to each franchise. Starcraft 2 doesn't need much introduction, but Supreme Commander 2 probably does. SupCom is a good game; it's actually put out by square enix, but it's the same head guy who was behind T.A. that got SupCom put together. The combat is awesome. Booming barrages of artillery, massive tanks, missiles, rockets, nukes, giant mecha, etc, etc. It's fun as hell. I haven't played SupCom 1; I didn't even realize it was a successor to T.A. until I saw an add for Sup Com 2. It's good, I enjoy it. The interface is slick and very intuitive, and the fact that you can zoom out to a full tactical battlefield overview is incredibly nice. There are some balance issues though, so it ain't perfect, and there need to be some more options in PvP games.
Starcraft 2 is pretty awesome also, although for different reasons. For starters, the single player game is fantastic. It's actually got a good plot, there are great cut scenes, and there's a system of purchasing specialized upgrades for your forces and choosing missions that's just awesome. Great job on the single player game.
But the combat... it's a little clunky to me. Sup Com 2 just plain has a better combat interface. Some of the restrictions on build queues and stuff in Starcraft seem artificial, designed to just force you to micro-manage stuff that's otherwise meaningless and automatic in Sup Com. I don't really like the restricted units for PvP; a lot of the older units from Starcraft 1 and the single player game aren't available.
So I was really kind of sour on Starcraft 2, for more or less the same reason I was down on Starcraft 1 and prefered T.A.
But I figured I'd give it a chance and keep playing before really rushing to judgement. And that's when I noticed something that will relegate SupCom to irrelevance and keep Starcraft 2 going strong for years and years to come.
Player Designed Content. In SupCom, there is none. You hop in and play, and beat the shit out of other players, and that's that. There aren't any custom maps, there's no extra map packs or anything. What you see, is what you get.
Starcraft 2, however, is now obviously designed with custom content in mind, and people are already taking off and running with it. I hopped into a custom game last night, and found a full-on four man tower defense mod beta map. All of the rules and systems had been retooled, and it was fun as hell. Still a little clunky, still needed some work, and the final tiers of upgrades weren't completely coded, but this was more or less an entirely novel game based off of the mechanics and visual elements from the core Starcraft game. That kind of flexibility is, in a word, awesome. In fact, they've even got a contest to design the best custom map for S.C. 2 already. I don't even think the game has been out for a month.
So SupCom is pretty much doomed, in my humble opinion. The lack of custom content is going to drive people away, as the game gets old and stale. I wish some of the cleaner interface options in it were transplanted over to Starcraft 2, but that tremendous customizability and the easy interface and ability to just hop into any type of custom map trumps anything Sup Com has to offer. It's a pity, because it's a good game, but it's just not going to hold people's interest.
So while Supreme Commander has some better interface options and cleaner combat, it can't evolve organically. Starcraft 2 wins hands down as a better RTS just for how flexible it is and how much cool content is going to come out for it.