I was in the closed beta, so I can safely say that people who complaint about base building are just whining. The main difference is that squads are the ones receiving upgrades which makes it imperative to keep your squads alive. On the flipside, all the upgrades you give to your commander are permanent: no mater how many times he dies he will still have the upgrades.
Both teams headquarters have very durable turrets, and the bases are hidden behind natural chokepoints. So the only way to get into one's base is to send in a dreadnaugh to destroy the turrets. But the enemy gets a huge healing bonus while near their base so there should be no cases where one can rush and take you over.
Squad size has been reduced for Space Marines, 3 marines with a possibility of 1 extra as a sergeant. People complained about that, but it shows how marines are supposed to be this elite force capable of withstanding armies. I had my devastator marines take out multiple squads of tyranids.
Overall, Relic tried to make the game go away from cheap rushing builds and turtling because either will result in a quick defeat. They also tried to make the game more squad oriented, you cant get away with just attack move ordering anymore. You must make sure that your squad is in the cover, pointing the right direction and always be ready to retreat. I believe their changes are good because not only they are more true to the tabletop but they also give a fresher way to fight. I had enough of DOW1 combat from the original game to its 3 expansions.
Just last minute thing, make sure to fight a few custom games against a cpu to get the hang of controls. There is no tutorial (i am guessing single player would be teaching you how to play) so you have to learn through trial and error. Or play Company of Heroes for some of the basics.
Proud owner of the following gaming devices:
PC, XBox 360, Wii, PS2, DS, PS3