Dawn of War plays well.
The campaign model in Soulstorm and Dark Crusade is pretty nice and has a good replay value. The neat thing for Dawn of War is that you can just get the latest and play all races in single-player mode. (For online play, you are limited to the ones you own - you can enter the game keys for other games you own to activate them.)
The gameplay itself:
You have infantry, heavy infantry, vehicles, d(a?)emon and commander/boss units, and of course buildings.
Each unit type has units it is more effective against.
Except most vehicles, units are organized in squads. You order them as one squad, and can order the squad to reeinforce itself to gain or replenish squad members (including squad commanders) and improve weaponry. You don't have to keep track of individual squad members.
Some commander units can be attached to squads (not all squads support this - especially teleporting and flying units)
There are hard limits how many squads and vehicles you can build. An important part in mastering the game is building a good composition of units that can deal with your foes.
Most infantry and heavy infantry units can capture resource points, relics and strategic points. All 3 let you gather resource requisition, which you need to build new units and for the modifications and squad reinforcements. Relics also allow you to build certain restricted items. Resource and Relic points can be reeinforced with buildings (that also improve your resource acquision rate.)
You have builder units that create buildings. Buildings are required for technical advancement and building new units, as to be expected.

There are also buildings to generate energy and to defend your base or resource points.
You need resources and energy for most advanced stuff.
Races have all different units and different strengths. Imperial infantry is weak and dies quickly, but it masses can be dangerous. Its vehicles are less numerous but very powerful, especially with the terrifying Baneblades. Space Marines are particularly good in close combat (even with some of their vehicles). The Tau are better at range.
Some races have slightly different resource models. The Necrons, for example, don't use requisition. Instead, the number of such points you hold determine your build speed and unit speed. (And you can reach a maximum of 100 % early on.). The races in Soulstorm gather additional "soul/faith" energy. Orcs also need "Waagh" and have to build according banners, and some units have Orc population requisites.
There are a few special super-powers, usually based around your commander unit. None of them work like Starcrafts nuclear strike or Command & Conquers Ion Cannons - you usually have to be close to the action to use them.
The "campaign mode" in Soulstorm and Dark Crusade doesn't follow an ongoing story-line. Instead, you just have a planet or system to conquer, and certain areas you conquer have a small story attached (like when you conquer a powerful warp demon artifact, or when you conquer a races primary hold-out). The strategy part of this isn't really very important - the nice thing is you get extra units (in excess of your squad caps, with some perks and weaknesses) when conquering individual sectors, and some special benefits when conquering certain locations (like more starting requisition, or an additional move/attack per strategic turn, or the ability to add some extra buildings to your starting base). The extra units are a nice way to allow you to go against heavier defended sectors. In a 'regular' campaign, you would have just gotten some starting units to defend yourself better in the beginning of a mission. (Like in Command & Conquer or the first two DoW campaigns)
The gameplay can be fast, and you need to keep an aggressive pace in expanding your territory and avoid enemy attacks. You need to continually build up units that complement each other. Finding choke points is important (thankfully, the maps are usually build in a way to support this) to defend yourself.
I own all the "expansions" (most of them are actually stand-alone games using the same or a slightly updated game engine.). I am not the kind of guy that is good at fast-paced real time strategy games (if it was me, there would be turn-based 3D ego shooters

), and while I would say that DoW is one of them, it works amazingly well for me.