I decided to download the rules from Fantasy Flight's website to get a feel for it before I was able to pick up a copy of the game. They are really good about making the rules to their games available for download before release, you just have to be a member on their site (it's free.)
I got pretty excited while looking through the rules. It looks like there are three Loyalist factions - Blood Angels, White Scars, and the Imperial Fists. There are four Traitor Legions - World Eaters, Emperor's Children, Death Guard, and the Thousand Sons. There are also a few other players as well - the Adeptes Arbites and the Adeptus Custodes. There are also two unit types that can fight for both sides - the Imperial Army and Imperial Tank Divisions. These two units can be corrupted and will then fight for Chaos.
As well as the above units there are also heroes. The Loyalists get Rogal Dorn, Sangunius, Jagahatai Khan, The Emperor, and the Fabricator General of Mars. The Traitor Legions get Fulgrin, Mortarion, Angron, Magnus the Red, and Horus. These individuals are represented by special cards.
The turn sequence in this game is really neat. It looks like it borrows a bit from Epic as well as other hex-based war games. Instead of trading off taking full turns there is more of a you-go-i-go type of play where units get activated or a card is played and then the other player performs an action. Where it differs from this formula is the initiative track.
The initiative track is used to determine who the current player is. You move you counter along the initiative track as you take actions. Whoever's counter is closest to the start of the counter is the current player and may take actions. When you perform most actions you will have to pay an initiative cost - you then move your counter forward that many spaces. When you jump a player that player then is closest to the start and it becomes their turn. Something else that happens when you jump a player is that combat is fought - so this is a very neat mechanic. There are also special tiles on the initiative track that let you draw cards and refresh your units on the board.
One of the major mechanics of the game involves orders. You have a hand of orders that you can play in several different ways. You can play them straight from your hand or you can play them from the board by putting them face down. You can have multiple orders in one map area so you can almost program your orders. What you can do with an order is pretty broad. It is how you move units, declare attacks, and many other options.
Now lets get down to the meat of things - COMBAT! Combat is very rigorous and has a nice concise set of rules. Basically you determine who is fighting, where, and where they came from. You then work out battle iterations - basically turns of combat. You determine how many iterations you have from the card that let you attack. You attack by playing battle cards. You draw battle cards at the start of a combat. To determine how many cards you draw you add up the ranks (1 -4) of your combatants and divide by two. Battle ends when you have reached the maximum iterations, one side is dead, or you run out of cards.
Working out an iteration looks pretty involved on paper but I think it won't be that bad. Basically you take turns being the active and passive player during an iteration. The active player tries to deal damage with cards and special abilites, and the passive player tries to resist. Just think of it like 40k initiative steps - the attacker tries to damage the defender, and the defender tries to save.
As you move through the iteration steps of the battle you will pass back and forth being the passive and active player.
Heroes can take part in battles. You draw Hero cards when they are involved. Damaging a hero is a bit different. There is a hero damage track on the board. All Heroes share the same track and move along it as they are damaged.
The gameboard/map looks really neat. There are several factories, defense structures, and the imperial palace that you place on top of the board - they stick up from it. These are not just cosmetic - you are trying to attack or defend these different locations. By defending a structure your units inside are able to mitigate damage that would be done to them.
There are also Orbital Bombardments, Defense Lasers, The Vengeful Spirit, crevases, and a whole host of other fine grained rules. I am going to have to wait until I get a game in before I really go over any of these finer points of the game.
All in all I am really excited about this game just from reading the rules. Can't wait to get my hands on the actual game and give all the bits inside a good once over. The game sounds pretty complex, but I don't think any of it will be too bad after one or two play throughs.