Its been ages since I've played DOW I, but as said above, DOW II is heavily based on squad combat, For MP, the only base you have is your "stronghold" which is where you order in units and upgrade it to get access to more units. The game is all about tactics and using the correct unit counters. There are 2 main game modes, Annihilation and Victory Point Control, the first one is pretty obvious, victory point is where each team has to hold the points on the map to cause the enemies "tickets" to count down, if you've played unreal tournament, its like the game mode "Domination" but RTS
I suck at explaining. Resources are still power and requisition and you hold points in the same way, but you only build on power nodes, requisition is just captured.
The SP was pretty good, you have 4 units which you can deploy to a battlefield out of a possible 6. The combat is good, and the item system is good, it feels a bit RPG'ish because your characters level up, have lots of armours and weapons which have level requirements and you can also use skill points which are similar to a talent tree. I haven't played Chaos Rising's SP but people say the corruption system in it was really good, you had to make choices based on your morals and then that changed the outcome of the game/story.
There is another game mode which is called "The Last Stand" which is quite a fun game mode, it has the items from SP and you control just a hero unit and you must defeat waves of enemies and survive till the end, the last stand is COOP, so 3 players team up to defeat the waves, each hero has its own roles, and within each hero, there are lots of builds to try out to change the role of the hero....
For example you can use the Mekboy and you can give him heavy armour, a health regen blade, and a bouncy shield to use him as a tank, or you replace the blade with a suppression gun, replace the heavy armour with a teleporter pack and replace shield with a heal, which then changes his role to a support gunner.
Overall, I think DOW II is a pretty good game, its quite different to other RTS's but it is good at focusing on Strategy and getting into the action, theres no 10 mins at the start while you build a base or whatever, you start with some units and you go off and fight straight away!