Well, you apparently can go from Crusader Kings, to EU2, to Victoria, and soon to HOI2 DD.
I really like Victoria. It's economy is far and away the most complex out of all of their games, and it's fun building up your empire. It takes a few play throughs to learn how to really industrialize, but once you figure out how to get that empire it's a lot of fun.
I have heard that there are plans to have a CD release of the expansion however.