I wrote a couple of articles a while back, on the actual units you may consider taking in a Horus Heresy list. The first two-parts can be found here:
Ok, so onto the crux of it, Rites of War. As most HH gamers should know, you should never let the Force Org Chart get in the way of a good, fun list. Rites of War are there to spice it up a little, they allow you to change how your army implements the FoC, as well as giving (and taking) rules from you. There are 4 main Rites of War listed in the HH book. These are unlocked by taking a Master of the Legion, typically a Praetor, Primarch (obviously) or some special characters.
Basic Rites of War:
Orbital Assault: This RoW basically lets you take drop pods and dreadclaws as dedicated transports instead of rhinos. The down side is, any unit that can't deep strike, or ride in a vehicle that can, can't be taken. Also, no fortification for you.
Armoured Spearhead: Rhinos become Land Raiders (for the right points..), if you tank-shock an enemy, their Ld is at -1. All infantry must be embarked on a vehicle at the start of the game. If you buy 12 marines and only brought them a rhino, I have bad news for you. If all tanks in your force are destroyed, your opponent gets a free VP. Oh, and no fortifications. Again.
Angels Wrath: All jump pack models gain hit and run. Rhinos now become Storm Eagles. Only jump units, fliers, skimmers and vehicles embarked on fliers may be taken. Oh, and a trivial side matter... no tanks at all, and no fortifications. Again.
Pride of the Legion: Veteran Marines and Terminators are troops choices, not only that, they MUST be selected to fill your compulsory troops slots. Command squads can take Land Raiders as dedicated Transports. Of course, the ever wonderful down side is if you lose all your veterans and terminators, your opponent gets an extra VP. You also can't take allies. Period.
As said in the past, RoW give you buffs, but they also take away options that can be quite hard. That's the penalty for fluff, and it's a fair one too.
Legion Specific Rites of War:
Here is where it gets interesting. I am not going to go into any great detail here, as they are varied, some haven't come out yet (we do only have 13 legions of 18 at the moment after all). The main thing to keep in mind when it comes to Rites of War for your specific Legion is that it's forcing you to play in a specific way.
The first example I will use in detail is my very own and beloved Raven Guard.
The long short of the Raven Guard Rite of War "Decapitation Strike" is that:
-all the models with the Legiones Astartes (Raven Guard) special rule get preferred enemies 'independent characters'.
-If this force is my Primary detachment, I may reroll for deployment and to see who goes first.
-Drop pods become dedicated transports for all the main foot-slogging units, i.e Tac Squads, Terminators etc. Deathstorm Drop Pods may also be taken as Elites, not just heavy. This probably has something to do with the limitations..
-You may only take a single Heavy Support choice.
-You may only take a single Consul as part of your HQ choice.
No Fortifications or allied Space Marines allowed. (but Mechanicum, Knights, Imperial Army etc. are A-OK)
So, what does this mean game play wise?
As you are limited in the HQ department, thanks to your single consul, and since you need a Master of the Legion to even run the Rite of War, my choice goes to Alvarex Maun. With the ability to have no-scatter deep strike and re-rolls for reserves in a force specialising in Drop Pod assaults, he comes in very handy.
Force wise, you are aiming to go for a lot of drop-pods, fliers etc. These can negate the loss of your heavy support elements by bolstering your firepower with their aerial prowess (Storm Eagles with melta/las are awesome for anti-armour whilst you machine spirit fire your missiles into infantry blobs). The key with Decap. Strike is to use it to take on characters and gain the bonuses of killing the enemy HQ. Against Mechanicum and Solar Auxillia armies, the loss of their general can be devastating, and I highly advise using a squad or two of dedicated character killers to 'off' them. A suggestion in this area might be to use Mor Dethyan snipers, and declare the marked target, for a turn of 2's to hit, 5's to REND preferred enemy sniping....
Characters and Rites.
Certain characters can have a massive influence on your Rites of War. Some restrict them, others can practically make the Rites of War redundant or allow you to essentially take two. Erasmus Golg of the Iron Warriors, for example, opens up Terminators as troops, making Pride of the Legion slightly pointless. Perturabo gives all of your Terminators deep strike without needing to take Orbital Assault as a Rite of War. It's good to know where these rules can stack, and combine. Michael from over at the Eye of Horus podcast uses the Stone Gauntlet Rite of War, which allows him to field toughness 5 breachers. Suddenly they are worthit, as opposed to being a 100 point more expensive and less effective tactical squad. By combining un-named characters into these units, he ends up with a list stronger than the sum of its parts. Keep this in the back of your mind.
Alternate Force Organisation Charts and Rites
So, you like the idea of running a Pride of the Legion force combined with an Alternate Force Org. Chart? Guess what? You cannot. Pride of the Legion only applies to lists built using the standard Force Org. Chart. I'm not going to tell you where it is written, but my challenge to you is to find it out for yourself, that way when somebody rocks up with a POTL list with 4 heavy choices you can shoot em' down.
Having a Rite of War is a great thing, it allows you a lot of options and gives you the ability to run really fluffy (and even competitive fluffy) lists, without having to proxy or make awful allied detachments. I recommend you play around with them and see what you can come up with, because there are some fantastic options.
All the photos in this post are from Inferno III, the full album is located on our Facebook page here.