Game progression is actually pretty varied for an RTS. During the first couple of missions you are presented with a live action cinema and then given a mission to complete. The missions range from escorting friendly units to sabotaging rival ships, as well (of course) as total annihilation of an enemy. After several of those operations, the plan of attack is up to you. You are shown a strategic map of Arrakis and can choose which territory you wish to capture. After that, the computer is given a chance to attack you or another House on the map.
You start off each map with one MCV, which expands to become the Construction Yard, where all the other buildings are made. Once that is constructed, the Spice Refinery, Barracks, Factory, and Outpost make themselves available for construction - giving you the choice to devote your research towards economy, offense or recon. Resources consist only of Spice fields located outside of the base and can only be collected with the Spice Harvester, which makes managing your economy very simple.
Harvesters are slow moving, but luckily they come with a Carryall, which flies them to and from spice fields. Harvesters come well armored, but if you neglect protecting them in mid-game they can quickly fall prey to a small rush and leave you without any money. On the whole, if you have played any of the Command and Conquers, you should have no problem getting into the rhythm of Emperor.
The units in the game are conventional. Westwood avoids trying to break their RTS mold in terms of innovation. The higher you go up the tech tree, the bigger the units are; and the bigger they are, the more "boom" they produce. Unfortunately, that's all they produce. Units are meant exclusively to kill other units. It's too reminiscent of Red Alert, where none of the units have special abilities like being able to slow down a pack of opponents or reducing the damage their weapons deal. It gives the units a bland flavor that really holds the gamer back from coming up with strategies more complex than pounding down the enemy's front door.
"Quick" is the word of choice when describing the gameplay. This is nothing like the turtle-paced Starcraft, where you spend the first five to ten minutes of the game twiddling your thumbs, waiting for things to get built. Most of the buildings, vehicles and infantry construct at lightning speed. After three minutes, you should have a strong economy of three spice harvesters and a militia of both high-level infantry and middle-level vehicles. After seven, the entire tech tree should be researched. Most of that is possible because you are given a huge amount of default money, so units and buildings can be queued up at all times. But if you are idling for more than two seconds, you are not playing the game correctly and your adversary will happily exploit that.
Perhaps the insane speed of the game is a result of the cramped nature of the maps. Most of the story-mode maps (and quite a few of the 2 player skirmish maps) are small, with the enemy right around the corner. Attacks are generally quick and frequent because the travel times from your home base to the enemy base are only a few seconds. And your Spice Harvester is often in plain view of the enemy's because the spice fields are practically next to each other.