The game that defined the genre, and a good reason to own a PC for gaming.
The value comes from the variety of units. There are tons of ways to win and compensate for an opponents strategy. Really, it's like a rapid game of chess where you are both shifting pieces at the same time. This is also one game that was better before the expansion (Yuri's Revenge).
Some highlights: using the Eiffel Tower as a weapon, sending heavily armored blimps (yeah, dirigibles) in to slowly slaughter the enemy, sneaking spys into the enemy camp, dropping terrorists into the enemy camp (this was pre-9/11), creating a "Chrono-Ivan"
The sounds are great, if dated. The Soviets truly sound depressed when you click them, and the Allied units are always crisp and well-trained officers.
Conversely, if you dislike RTS games, you'll hate this to the core. Lots of resource gathering management and base defense. You'll need to build up a tech tree to access the better units, and need cash to then build them. The fast pace can be offset by an interminable wait to produce a particular tank or building.
But cross-breeding units is truly one of the best aspects of the game.