I think the Mechnicus is pretty cool, or at least the aspects that aren't "MY MACHINES!!!" They're pretty much the only faction that really does stuff with Machine Spirits, their fundamental religious strictures are interesting, they're pro-human, and their armed forces are super cool.
Skitarii
are
fucking
badass.Like those dudes
prance around on two legged insect walkers (like, holy shit, I wanted to have Imperial Guard rough riders Winged Hussars but they... woah), shoot people with pure radiation and their
gun design is fucking cool. Also robes and hoods and armour all around. Ever since they came out I am utterly confused whether Imperial Guard is still my favourite faction and
I liked the Mechanicus armed forces even before, due to how cool they look while they laugh at your inferior technology.
I think the Mechnicus is pretty cool, or at least the aspects that aren't "MY MACHINES!!!" They're pretty much the only faction that really does stuff with Machine Spirits, their fundamental religious strictures are interesting, they're pro-human, and their armed forces are super cool.
Are they really pro human though? Yeah they support the human race but they're ultimate goal is to divest themselves of their humanity. But they've always seemed one edict away from hatin' humanity.
Kind of. They're still more or less human (or at least they usually have at least 1% human body, usually some portion of the brain) and they always were more of "improve" than "remove", and even then Adeptus Mechanicus aren't all focused on machines, since they dig technology, and biotechnology (CLONING VATS ANYONE?!) counts... Also, as much as they would want to, they can't really make mechanical babies (though, IIRC, I remember there was an canon story about Adeptus Mechanicus couple and they basically grew the baby in a vat and enjoyed looking at it, which is either unbeliveably creepy or... kinda cute, I guess?), at least not yet.
Aaand, considering that their state is way worse than they would want anyone to know, they can't really exist without Imperium, and Imperium cannot live without them. They might be two different institutions, but in the end they're all humans and work for the survival of human race, as that is the core of the Cult Mechanicus.