In my opinion, Jeremiah Kraye epitomizes what Warmachine casters should do.
It's not because he is powerful, or game breaking, it is for one simple reason.
He changes how the game is played and how you build your lists completely.
No one plays like Kraye, he has a truly unique feel and set of rules. And that is mostly from his Iron Horse rule that turns all warjacks into cavalry.
Now I get that not all casters can have such a dynamic change to the rules, but I love Kraye for this reason. Some casters feel a little "generic", but I never feel that with Kraye.
One of the things I love about Warmachine is how your caster selection changes your game plan. And there are few examples of a caster that does this more than Kraye.
His spell list supports a lot of move and maneuver tactics, as well as straight down your throat threat.
Light jacks get a light cavalry move of 5" after that activate. This adds in a load of funky "move, shoot, move" options that few others can replicate.
Hunters become even more annoying with this, and minutemen get off the hook with advance, jump pack and light cavalry moves.
Add in "full tilt" a spell that doubles a warjacks speed if they don't shoot and the ability to give all jacks pathfinder and you have some CRAZY movement potential.
(Watch you opponent have sad face when you move a minuteman 12" as an advance, and then jump pack into his character unit and kill them with flak field. Poor poor black frost shard thought they were safe behind that forest)
Heavy jacks also get ride-by-attack, which allows them to move, attack, and continue moving. They also get mount attacks and a cavalry charge bonus. I'm yet to pull off the "cyclone ride-by double-handed throw", but I love that it's an option.
All these bonus mean you have to relearn to play with Kraye, and he is an exceptionally fun caster to play.
I run him light on infantry and use focus easy jacks (and stormwall).
The current list I use has Stormwall, multiple hunters and Sentinels, a minuteman and rangers.
It can put out an insane number of boosted shots to clean up infantry, and a Full tilted Collosal is a scary threat on his feat turn (17" threat, charge for free, boosted melee attacks, 5 pow 20 fists roll 6+3d6)
Sure, he may not win all the games like an eHaley, but he's normally a lot more fun to play.