I bought both games several years ago at full price (~$40-50 a piece). I'm an avid RTS fan. Started with WarCraft 1, WarCraft 2, C&C (the original), Red Alert, Starcraft, TA, etc... too many others...
Recently I've played C&C 3, Dawn of War (Original, Winter Assault, Dark Crusade), WC3, etc...
AND SupCom owns them all hands down. I hated it at first because it is so massively different from all other RTS's in the sense that all other RTS's have fixed cameras that restrict your field of vision. Other RTS's are just very localized and your zoomed in all the time. This has a certain feel to it that TA really does not at all share. This made me hate TA at first until I saw a friend play and then I understood the scope of the game / combat.
Other RTS just doesn't have the scale that TA does. Also it seems like there is no variation to strategy with those other games in online play anymore. DoW used to be a lot of fun originally, but after a ton of patches and as the player base becomes more experienced - ultimately there is only one strategy for any given map. So then the game just turns into a twitch fest. Other RTS's share that problem. SupCom really doesn't. There are soo many variations in strategy. Sure there are a couple main ones that a lot of people use in multiplayer - but man it is totally wild - soo many different strategies could work on most maps - from rushing, to sneaking tactical nukes by their base, to air drops, to tech rushing, to dominating the air, to controlling the seas.
SupCom is a RTS on a massive strategical / tactical scale. Played properly you will spend most of your time zoomed out watching the whole map. This style of play is massively different from other RTS's with their crappy fixed cameras. The SupCom camera / zoom owns so much. I can never play another RTS that doesn't have it again. I can control 2-3 massive engagements at a time pretty easy. Other RTS's with their crappy fixed cameras - makes it turn into a twitch fest trying to control everything. I hate that. If i watch twitch play I'll go play FPS's. I want _strategy_ and _tactics_. SupCom has that and is all about it.
Lots of strategy / variation. Tons of units. Graphics are awesome. There are only two downsides to sup com:
1) Multiplayer community is not that big. You can only really find games during prime time. Although FA is better.
2) Game is a beast as far as computer specs go. You need a fast machine. You really should have somewhere around an e6600 (dual core 2.4 ghz), 2+ gigs ram, and a decent graphics card (like nvidia 8600+) otherwise the game will play like complete crap on bigger maps / multiplayer.
Awesome game - best RTS out there hands down. All other RTS's seriously suck in comparison and I can never go back.