The rules for this Formation are solid, but not game changing. All units must start in reserve, and the jump packers have to deep strike. The whole formation arrives at once, and you get to re-roll its reserve rolls. Every unit gets Crusader, which is a nice bonus to such assault oriented squads. Crimson Thunderbolt gives any unit disembarking from the Stormraven Rage and allows them to re-roll failed charge rolls. Finally, Rain of Bloodgives any unit arriving from deep strike Counter-attack and Fearless until the start of your next turn.
This is an all-out assault formation. The main brunt of the assault will be units in the Stormraven, which should be the Vanguard Veterans and Furioso. The Death Company already has Rage and the Assault squad comes with jump packs and don’t have the hitting power to capitalize on Crimson Thunderbolt. Rain of Blood makes the deep striking squads more resilient to assault, but they’re still vulnerable to being shot off the board. If it arrives Turn 2, the whole formation should be ready to assault Turn 3, and that’s a lot for an opponent to deal with.
There’s not much fat in this formation. All the units help its overall goal of slaughtering enemies in assault. It does rely on the Stormraven hovering to drop off assault units, something I am normally loathe to do. However, the units it carries and the special rules that it grants make it worthwhile in this case.
I would keep the Assault squad and Death Company small but appropriately equipped for this formation, while the Vanguard squad can be larger and more heavily armed. The Furioso should of course be armed for assault, and the Stormraven should be as cheap as possible because it will almost certainly be shot down immediately after dropping its cargo. I know I sound like a broken record about this, but the biggest downside is the lack of Red Thirst. At least they don't miss Descent of Angels too much because they automatically re-roll their Reserve rolls.