I've played Dawn Of War I quite some time ago but never the expansions. Are they any good? Also, what about Dawn Of War II? Is it similar to the first one?
You already got DoW 2 response so I'll add DoW expansions one. They are mostly worth it. Winter Assault is a lot like vanilla game but you can play for 2 sides and 4 different factions. So if one likes vanilla, WA shouldn't be a miss.
Dak Crusade is great and in most aspects better than vanilla game. You can play any of 7 races and on planet map you select regions to attack and your goal is to eliminate all opposing factions. So it offers open campaign with free choice of missions. It is not story heavy at all, though and besides stronghold assaults all missions are very similar and with no other win condition than to eliminate ooponent.
It also offers some basic leader level ups.
Soulstorm is in similar vein as Dark Crusade but it is unbalanced and overall not good and it is widely recommended to avoid it.