If you ever wanted to command a force comprising of a ridiculous amount of units, in a futuristic world where the art of war has been changed by advances in technology, then you'll probably want to check out Supreme Commander.
NB. Remember to use the following code to pick up the game at the advertised price: STUDENT10%
You can get hold of a copy of the game on the PC for £1.79 from The Game Collection, which'll save you just over £2 on the next best offer of £3.93 coming in from The Hut. Also, even if you can't use the code, you'll only have to pay £1.99, which isn't all that much when you think about it.
You'll be able to choose to fight as one of three races, which at the very least increases the longevity of the single player if you're not particularly fussed about each race's background.
Like the majority of RTSs out there, your ultimate goal is simple; form a superior force to smash your enemies with whilst fortifying your bases so that they can be easily defended should your foes foolishly decide to attack you.
The scale of the battles is pretty huge and you can quickly move from observing and giving orders to single units to viewing the entire battle field with a simple flick of your mouse's wheel. There are also multiple ways for you to crush your enemy, seeing as you can attack them with either ground, naval, or arial units.
RTS fans should love Supreme Commander and I think even newcomers to the genre'll get addicted to the futuristic warfare after a battle or two.
Thanks to andywedge @ HUKD