If there is any one reason why the RTS genre is as popular as it is today, the answer is unanimously Command & Conquer. Even after all these years since its release, it still stands out as a fun and well balanced game due to design features that were well ahead of its time.
Anyone who has not played Command & Conquer should be ashamed of themselves. Long before Starcraft, World in Conflict, Act of War, and all of today's modern real-time strategy games, a small and up-and-coming game studio known as Westwood unveiled what would soon become the world's first true RTS game. It featured all of the things we've come to expect in a strategy game: base building, resource management, multiple units with strengths and weaknesses, a captivating story, live-action cut-scenes, and multiplayer capabilities. Oh yeah, should I mention it was released in 1995?
Command & Conquer is set in an alternate time-line where a mysterious meteor has crashed into Earth containing crystals known as Tiberium. Scientists have only begun researching the uses for Tiberium, though its primary application is in regulating the world's economy. A private organization known as the Brotherhood of Nod currently leads the way in terms of research, giving them a powerful edge financially and militarily. Recent power struggles have occurred between Nod and the Global Defense Initiative, a conglomerate of countries hoping to bring peace. It's up to you to choose a side and help lead it to victory.
Each game usually starts you off with a set of units and a Mobile Construction Vehicle (MCV) which you maneuver to a good spot for a base and deploy. With the MCV deployed you can now begin building structures to aid you in your fight against the enemy. There's a pretty large list of buildings available, such as the barracks, war factory, refinery, guard towers, etc... What makes C&C so fun to play is its balance in gameplay. Both sides have their pros and cons. Nod forces are cheap but weak, while GDI units are expensive and strong. This means that you can't always use the same strategy depending on what side you choose.
The graphics are pretty good for their age. Each unit is easy to discern and the HUD is rather efficient in terms of usability. The music is top notch, being composed by Frank Klepacki and containing a nice mix of rock and electronic sounds.
Here's what SoupHat had to say after I used my commando to annihilate his base:
Ah, Command and Conquer: one of my first forays into the real-time-strategy genre. A great game at the time of its release, it remains equally fun even now. The gameplay is essentially the same as more modern RTS games. However, I do have two complaints. One is that the pathfinding is sometimes really sketchy. My harvesters often ventured off to the middle of the map to find Tiberium instead of simply mining the field that was directly next to my base. The other problem is crates. Crates are boxes that randomly spawn on the map which give you a reward such as money or an ion strike when you collect them. These are usually a great thing, but sometimes they blend into the scenery and are hard to locate. Another thing to note is that Command and Conquer Gold had difficulty on both Vista PCs I attempted to play it on. On both it stuttered like it had multiple speech impediments. I finally had to install it on a virtual machine running Windows XP under vista to play it properly.
Command & Conquer still lives up to its name, even after all these years. If you have never played, download it now!
NOTE: The original game was released by EA as freeware but required you to either burn it to a CD or mount it with an ISO mounter. I've gone through the trouble of removing that requirement with the aid of a no-cd patch and two custom launchers I wrote in C++. Each launcher is tailored to a specific campaign (GDI or Nod) and, while you can use either launcher for both campaigns and multiplayer, you won't be able to view the live-action mission briefings unless you use the launcher that corresponds to your faction. Don't worry, it's easy. I've also installed a patch that allows you to play with a friend over LAN. For those who know what Hamachi is, that works too. And for the record, SoupHat and I spent HOURS before getting multiplayer to work. You can thank us later.