Late last week, the crew at Ensemble left us a present and we didn't even notice it. The company unlocked every unit and structure in both the UNSC and Covenant field manuals for Halo Wars. If you're hankerin' for some Halo Wars, you might want to browse through each field manual. After all, the game is only a few months away, so you might as well start planning your strategies now.
One strange note, we're not seeing any Brute units for the Covenant. We know they're in there somewhere though. Upgrades from Elites perhaps?
Source - UNSC Field Manual
Source - Covenant Field Manual