Overall, I think these paintjobs are very focused on the faces of the Praetorians. They are rather expressive and characterful minis, and they have such nice style in that Imperial Underdog kind of way. Here is a good shot that shows off the face quite well.
This squad of Praetorians were converted to wear carapace armor- that way they can be used as storm troopers or veterans.
It was a simple case of swapping out the sentinel driver for the upper body of a Praetorian gunner. I think they designed sentinels that way on purpose, because this way every Imperial Guard regiment can have sentinels attachec wthout a lot of work.