I don't know much about them but I would like to hear your thoughts on them.

Superer super soldiers as Arch Warhammer sais it so well, I think they are a very short term solution that's I am expecting it to backfire on the Imerium and probably prudently die off because they were a stop gap measure for the worst of situations and probably on't have the Space Marines longevity have. I wouldn't be supposed if they happen to have Thunder Warrior components to them with the expected results that entails.

Pretty cool in my opinion; in the board game at least the marines are very average since they tend to be what everything else is compared against. The Primaris try to make to space marines feel like super soldiers again. They do need to actually decide what they are doing with them though; originally they were supposed to be immune to the genetic failings of the chapters except, whoops they ignored that almost immediately.

as miniatures, really good, as lore... well they just shoehorned it badly. After 30 years of established lore and stuff, they come with this.
Ohhh really NOBODY noticed all those bodies? NOBODY noticed what Cawl was doing? in 10 MILLENIA?!. Not buying it, they could had done many things or at least try to brew more palatable lore for them, instead they did this....

Primaris Marines Iron worriers, there a interesting thought. What do you think would happen if a group of Primaris Marines made there way to ever join or fight the Iron Worriers.