The setting is fantastic (warring nations, ancient secrets, unusual races, intrigue, adventure, and weird tech) and Mosternomicon is one of the best monster books ever and should be the standard for all such works, it has its own on going magazine for support and between Warmachine, Hordes, and the IK specific ones some of the best miniatures you are likely to find for such a unique setting. That being said I have two problems with the game. First is minor and can be ignored at your leisure, their adds and slogans are not to my taste; but thats just my opinion and they are not so bad I don't buy their stuff when I have a mind to do so - but it might keep me from recommending them to some people. Look at it yourself and make your own call.
More worrisome, however is that some of the mechanics, particularly some of the setting specific classes and the complexities of item creation, are a bit 'wonky'. However, I think all of that is fixable if you have a group ready to play it. I suggest reading through it, paying careful attention to mechanical issues, and then decide how you want to handle it. A good way of doing so would be say "no mekanika for PCs" and if you had someone who was just dying to play a creator of magic items use the Artificer from Eberron and spin the flavor of it to accomidate the more "full metal fantasy" aspects of the setting. Take the Battle Sourcer from Unearthed Arcana remove the single martial melee weapon proff and change it to Exotic Weapon Proff(Pistols), grant it a pistol as an item familiar and let it treat the pistol as a required arcane focus that substitutes for any material components less that 1gp in value. Give it something like the Arcane Archer's Imbue Arrow ability, say with the ability to imbue a touch spell at 2nd, an area effect spell at 5th (all with a spell equal of one level less than the highest spell level known, and it must be a spell known so nothing from scrolls etc). You can add in Seeker Arrow (15th), Phase Arrow( 20th) or maybe a special magic item creation ability that allow the class to make bullets that can be fired by other characters that have magic effects (around 10th).
The reason firearms are exotic in the setting is that they require special skills to load and handle as the explosive components are actually alchemical items more than gunpowder. I say keep that aspect as it works in the setting, but be sure to allow anyone with the feat access to the skills.
I agree the person who seems to be upset by someone named 'Mark' - stay as far as humanly possible from the Witchfire Trilogy. If someone gives it to you, give it back.