The below is the Dire Avenger entry for the Biel-Tan in 4th Edition Project. I thought it might be useful. It may be skewed towards Biel-Tan, so that that into consideration. I am adding additional information to this post, despite its date of last post, because it is now stickied.
Dire Avengers:
Well here we are, the first troops choice. I will speak more in detail later about the troop choices as a system, so will try to give no more than a passing mention of that here. As with all of the aspects, the Dire Avengers were refined or enhanced towards their role. They are no longer just glorified guardians, but masters of the shuriken. The previous role of the Dire Avengers was to take down light infantry and horde units primarily (as simple as ten Guardsmen, or as prolific as 20 Shoota Boys or Genestealers) and to tie up enemy squads in close combat until something tougher arrived. The role has not deteriorated. With the new exarch abilities and equipment, as well as possibly help from Doom, this squad has the capacity to cause some hurt to tougher targets such as Tyranid Warriors, or even monstrous creatures. Also it is no longer just the Exarch that has defensive qualities. There aren’t any direct changes to their points or stat-line but the new equipment and exarch abilities make the squad.
Shooting/CC mix:
By themselves the Dire-Avengers are still a cheap and effective unit for taking down light infantry. Against units like IG squads, their better saves and WS will tend to allow them to take down equal sizes of guard in the end, or when shooting then assaulting capable of wiping smaller squads and consolidating into others without much difficulty. Against tougher opponents such as Tyranids/Orcs you will need a numerical advantage to execute this kind of attack. This is where the exarch comes in.
With bladestorm a squad is able to boost their firepower for a turn and quickly reduce the numbers of the opposing squad, making it much more likely to gain numerical superiority for finishing a squad/gaining safety in CC. The exarch’s double shuriken catapults also help, giving the squad 5 BS5 shots which if against light infantry, especially if not in cover, will claim a lot of lives. The typical offensive exarch is bladestorm+double shuriken catapults. Whether going for wiping out a dangerous squad on the go (HQ squads, CC squads, or even looking to hurt an MC), or weakening a tough squad before initiating other roles, as discussed below.
With the increased range of the shuriken catapult and these new and powerful exarch abilities/options the Dire Avengers have increased their capabilities in defending objectives, wiping out both the mundane light infantry, and tougher/larger squads of light infantry. They also have capabilities for putting so many shots on tougher targets such as meq/MC’s to cause realistic damage (not wiping, but causing meaningful wounds that with combined fire could take it down). A few months ago my Dire Avengers bladestormed a hive tyrant, causing 2 wounds, and on the charge between them and the farseer, they killed it.
CC lock:
Here the Dire Avengers gained a big boost. It does still require the exarch to reap these bonus utilities, but they are much stronger than the third edition abilities. This role of the Dire Avengers is constituted by the Avengers locking opponents in CC, either to strangle them to death, slowly cause deaths and try to force sweeping advances, or to hold the enemy unit until tougher support arrives. This is one of the main roles I will speak about in the article section of coping with the troop changes.
Defend is the most massive ability, making it so that they can charge CC intensive units, take away charging bonuses on those intending on joining its combat, or nerfing characters in CC. This greatly slows down incoming damage to them, sometimes making it as if they were fighting half as many foe’s. The Shimmershield may seem like a rarely used item, but it depends on the role in which you use your Dire Avengers. If you are fighting enemies with power weapons, MC’s, rending, etc, and wish to use your Dire Avengers in this locking role, it can be quite useful, but it is definitely not a “don’t leave home without it” piece of equipment, but can be essential if you have that specific role in mind.
The CC lock role of the Dire Avengers is one of the most useful roles for the Dire Avengers, and is one of the most crucial it will have. It has become infinitely better at it than in the 4th edition. Some people elect to take shooty Dire Avengers, or locking Dire Avengers, and some that take multi-role Dire Avengers. This is where most of the arguments come from when people say, “is this item worth it?” As always in 40k, and the Eldar in particular, rarely are there bad items, merely good or bad roles and situations for them. I would say that the Dire Sword is no better than it used to be, its only benefit is the extra attack from 2 CC weapons, but the double shuriken catapults are cheaper and will likely cause more wounds than the extra attack in CC. The power weapon may be better for against MEQ targets, but otherwise double cats seems to be the best in any exarch situation.
Overall the Dire Avengers have increased their ranged capabilities immensely against tougher or larger light infantry targets, and because of this increase have gained tougher targets such as smaller meq squads (or larger with combined support), MC’s, rear/light vehicles, etc. One could say there was a locking role before 4th edition, but it has become so infinitely more practical that there is a definite and necessary role in the Biel-Tan army for it. More on this later in the article.