Ok we are getting some details on some of the weapon characteristics we've been seeing.
Weapons are not a type, like Assault/Rapid Fire/Etc, they have those as characteristics. So as see here with the bolt rifle, it is Assault and Heavy. Assault lets you still fire if you advanced, and Heavy adds plus one to the Hit roll if you didn't move.
Critical Wounds are rolling a unmodified 6 to hit. So the Assault Cannon jumps straight to mortal wounds if you roll a 6 instead of moving on to wound and save.
Sustained Hits on the other hand add X number of hits for unmodified 6 to hit Critical Wounds.
So I think its D6+2 for Melta range, not 2D6.
Twin-Linked is built in wound rerolls.
Not shown but stated, Hammerhead Railgun is Strength 20 and isn't the highest strength weapon in the game.
Also on the pervious mentioned open top rules, its not full firing for transported units. Transport have a Firing Deck X stat, X being how many models with in the transport can fire. So only 2 units in a Rhino can fire out of it.