as an IG fan I am missing the orders and doctrines that allowed you to tweak your regiment towards a specific style reflecting the variety to be found in the Guard.
In fairness, this is one thing I like with the Unbound idea - I know there'll be plenty of people who go "Yay! I will take Five Heldrakes!" but they're tools and I don't have to play them.
What I wouldn't mind having a try at is doing the wierd and wonderful - like a guard cavalry platoon, or doing a deathwatch kill-team by buying 10 captains/librarians/etc as a 1500 point force.
One bad bit of news - it would appear that the background section in the main book has been written by Ward. Yay.