I like the general design of Primaris Marines but they are looking a bit bland for now. I guess it's so GW has a new model line for new player but still. Ah well it looks like the Chaos models go the exact opposite direction (more details everywhere) so I'm not mad about the bland Primaris models. Can't wait to see new Emperor's Children models.
Looking at that leak around the web, it's now very clear that these are starter-set rules.
If these guys are in larger squads, and come barreling in via Infiltrate or aboard a Primaris Rhino, you should be afraid. The starter set rules are junk, but in the real codex these guys should be quite good.