The Fist of Medusa Strike Force is available to armies of the Iron Hands and their successors. In general, it accentuates the already considerable durability of Iron Hands, and I think it will prove to be one of the strongest Space Marine detachments.
It brings 3 Command Benefits. Logical Commander allows your Warlord to take an extra Warlord Trait from the Tactical or Strategic Tables. An extra Warlord trait is always handy, and being able to take it from the very useful Strategic table is amazing. Other armies pay for Relics (such as the Finkin' Cap and Veritas Vitae) to get this benefit and consider themselves lucky. Reject the Flesh, Embrace the Machine grants any model in the Detachment +1 to their Feel No Pain rolls while within 12" of an Independent Character from the Detachment. This grants most Iron Hands a standard 5+ Feel No Pain, while a Command Squad gets a 3+ Feel No Pain and a character with the Gorgon's Chain can have a 2+ Feel No Pain. Space Marines don't get any tougher than that. Roused Machine Spirits grants Power of the Machine Spirit to vehicles in the Detachment within 12" (or while carrying) an Independent Character from the Detachment. This makes the vehicles extremely flexible, able to divide fire or maintain their firepower when shaken or stunned.
The Fist of Medusa is composed of 1-2 Core, 1+ Auxiliary, and 0-3 Command choices. This gives you an extremely flexible Detachment within the Formations allowed. There are three available Core Choices. The Battle Demi-Company is the standard Core, allowing you to flood the board with Objective Secured units. The Stormlance Battle Demi-Company is shared with the White Scars, and allows your units to run after shooting, including getting back on their transports, as well as re-roll missed to hit rolls when shooting at enemies controlling an Objective. This seems a bit ill-fitting for the Iron Hands method of warfare, but it does require all units to be mounted in a transport, so I guess that's what they were going for. Finally, they can take an Armored Task Force, allowing the Detachment to be built around a core of Tanks.
The allowed Command choices are the standard Strike Force Command, Reclusiam Command Squad, and Librarius Conclave. You can include up to 3 but don't have to include any, so you've got a lot of flexibility in how many characters you bring. Given that most of the Detachment's benefits are auras around Independent Characters, you probably want to bring a fair few.
The Fist of Medusa has a pretty standard selection of Auxiliary choices, including the 1st Company, 10th Company, and Armored Task Forces, as well as the Storm Wing, Anti-Air Defense Force, Suppression Force, Centurion Siegebreaker Cohort, Land Raider Spearhead, and Strike Force Ultra from the Space Marine Codex. They also have access to the very aggressive Skyhammer Orbital Strike Force and Skyhammer Annihilation Force. While these Formations are great for taking the
fight to the enemy, they will be isolated from the rest of your force and won't be able to benefit from the auras surrounding your Independent Characters, at least not initially. Be careful how you use them. I see the Fist of Medusa Strike Force operating similar to a Necron Decurion, staying together so that their overlapping auras will provide incredible durability.
The Fist of Medusa can also take the Raptor Wing, which is a great way to add flyers to your army while ensuring that you don't have to worry about poor Reserve rolls. Like the Sternhammer Strike Force, the Fist of Medusa can also add some single units without any Formation benefits. Honored Ancients allows you to add a unit of any type of Dreadnought while Iron Guardians consist of a Tactical squad and a Dreadnought of any type. I can't see many people taking Iron Guardians, as you already have access to as many Dreadnoughts as you want and most players aren't itching to take more Tactical Marines, especially after those required by your Core choices.
I can see two ways to play the Fist of Medusa Strike Force. The first is as a death star army. A Command Squad loaded with a bunch of characters, preferably on bikes, will be very tough, rivalling the best death stars available to Space Wolves and Dark Angels. The alternative is a mass of tough, Objective Secured Marines, able to soak up the best damage the enemy can put out while holding onto important parts of the battlefield.
Warlord Traits
Adept of the Omnissiah gives your warlord Blessing of the Omnissiah so that he can repair vehicles. If he already has that ability (as in he's a Techmarine), he can re-roll failed repair attempts.
Will of Iron grants your Warlord Fearless, which is quite handy to make sure an important unit will never fall back.
All Flesh is Weakness gives your Warlord +1 to his Feel No Pain rolls. Stacked with all the other bonuses to Feel No Pain available to Iron Hands, this will make your Warlord very tough to kill. This is the trait that you're looking for when running an assault oriented Warlord.
Student of History allows your Warlord to choose to fail any morale test he takes. This allows you to have a slippery Warlord, able to fall back from overwhelming enemy force. It's not as reliable as Hit and Run, but it can be used to fall back from shooting attacks, which can rob the enemy of assaults in the first place.
Merciless Resolve grants your Warlord and every unit within 12" Crusader, making them a bit faster. Crusader isn't an amazing rule, but being able to grant it in a bubble allows you to benefit all of your assault units.
Target Protocols is one of those rare HQ abilities that help in the shooting phase. It allows your Warlord and any unit he joins to re-roll 1's to hit in the Shooting phase. If you're running a support HQ, this is the trait you want.
I think this is a pretty strong Warlord Table. The only trait I really wouldn't want is Adept of the Omnissiah, as it's only useful on very specific characters. Most of the traits are really helpful to most Warlords, especially aggressive ones.
Gifts of the Gorgon
The Mindforge Stave is available to Librarians, and is essentially a Force power fist. It's not too expensive, and it would be a great way for your Librarian to take on monstrous and gargantuan creatures. However, it means that your rather squishy Librarian will be striking last, so you need to choose your match-ups carefully.
The Axe of Medusa is s melee weapon that grants +2 S and AP2, and is Master-crafted and Unwieldy. It also has Severing Strike, which means to hit rolls of 6 get +4 S rather than +2 S. It costs the same points as a power fist, but is weaker than a power fist except when it rolls a 6. The only advantage is Master-crafted. It's certainly not a horrible use of points, and will be better against T4 and weaker targets, but a power fist will generally be better against tougher opponents.
The Ironstone grants an 6" aura that allows your Tanks and Walkers to pass their It Will Not Die checks on a 4+. If they roll a 6, they also get to repair a Weapon Destroyed or Immobilized result. This is extremely strong for a vehicle heavy army and is a perfect Relic for a Techmarine on vehicle repair duty.
Betrayer's Bane is a combi-melta, but both parts are Master-crafted and the melta can be used as often as you want. It's expensive, but if you were planning to take a combi-melta on a character, Betrayer's Bane is more reliable and multi-use.
The Gorgon's Chain is the Iron Hand version of the Shield Eternal. As long as the bearer hasn't suffered a wound, he has a 3+ invulnerable save, +1 to Feel No Pain, and Eternal Warrior. If he takes a wound, he loses the bonus to Feel No Pain, and 2 wounds lose Eternal Warrior. If he takes 3 wounds, the invulnerable save is reduced to a 4+. While it's effectiveness is reduced when the bearer takes wounds, the Gorgon's Chain is better than the Shield Eternal when the bearer hasn't taken any wounds, and is equivalent when he's taken a single wound. Given 2+ Feel No Pain, it will be really difficult to take that first wound off the bearer. The relic is perfect for an assault oriented Captain.
The Tempered Helm allows all friendly units within 24" to use the bearer's Leadership for Morale tests. In addition, he can choose a single friendly unit within 12" to re-roll 1's to hit in the Shooting phase. Though somewhat pricey, The Tempered Helm is a great add on to a support character like a Librarian.