Those are grav chutes, they let Guardsmen jump out the back of a speeding Valkyrie/Vendetta like airborne rangers and land without breaking their legs. It does mean that IG can reenact Operation Market Garden though.
Necrons. I was in love of them, untill they got new codex. So, now I want to see Immatetium's infants, Deamons of Warp! Who's bad?
Adding guards would be nice. Lots of infantry spawns and... Tanks!!! Probably even Manticores and stuff. That's how war should really look like.