This is one of only a few named Mechanicum independent characters. His background is certainly odd -- not only was he power hungry and very skilled in the ways of war and war machines, but in a brutal combat with some really strange xenos, most of his organic self was liquified. What remained trapped in the logic circuits rebuilt his body (using stolen parts no less) and as a result his peers contend he is well on the way to being completely mad. Naturally, his home Forge World sided with Horus as he was their patron.
This guy brings the kitchen sink to the battle field. Not only has he a somewhat standard power axe, but he has a whole heap of interesting upgrades including (but no limited to) graviton imploder, repulsion shield and haemonculite cyber-corpus! What are they I hear you ask?
Well, the repulsion shield provides what is basically a 4+ invulnerable save to S=6 or better incoming fire. But this comes in to play when he is hit - not wounded. It gets better though. On a roll of a 6, the shot is fired directly back at the shooter!
The cyber-corpus is basically his life support vessel. He is a hulking monster of metal and robotica on the battlefield and everything in his stats and equipment is related to this. In addition, he gains a 5+ feel no pain roll.
His emergency teleport protocol can transport his organic remains away from his cyber-corpus when he loses his last wound on a 3+. The corpus then explodes like a vehicle and the enemy gains no victory points for slaying this warlord. Crafty indeed!
This guy has a huge points cost. I think we'd only want to use him in games above 1850 points if there wasn't a good reason to not use him at a lower points. The only other real weakness is his 3+ regular armour save. Why oh why is it not listed as 2+? Even with 4 wounds and T=6, the 3+ save is not quite what it should be. At least he would be instantly killed though. But he is vulnerable to fury of the legion style attacks that will have a heap of small arms fire coming at him.
I see Satarael as a swiss army knife commander -- and a monstrous one (literally) at that. He's pretty good at everything but not obviously excelling at a single thing. He has the power to troll enemies with his emergency teleportation tactics and he has the implacable advance warlord trait.
I personally see him as a multi-pronged threat. Place him in an army featuring robot automata and other strong threats and you have the basis for a sound force.
For me though, I think I'd sooner construct a Magos Prime in his stead so that I can specialise my forces a bit more.