It really is an incredible game. I've played a ton the last couple days.
They've done a great job with the single player campaign, and have added the ability to play custom 1v1 / 2v2 / etc...against A.I. of adjustable skill. There are also custom tactical challenges, where you're given specific units and must devise the exact counters to incoming enemies.
There are definitely some changes from prior Blizzard RTS games. Yes...just about everything is now tied to Battle.net. If you want to play with your buddies, you create an arranged team game over BNET, and can then play agains the A.I., or other teams.
The biggest...funniest thing...is that when you first log in, it tells you to create a character. This name will be tied to your CD key. It's your multiplayer ID, forum posting name, and the account that all acheivements and single player progress is tracked under. It's a one time shot and is not changeable. I simply chose "Jeff" which I'm fine with, but so many people are complaining that they thought they'd be able to change it. There are tons of permanent accounts named: "Test123", "asdfjkl;", Practice1, etc...