golden rule #1; just because assault marines are now a troops choice doesn't mean you really should go hog-wild and ignore your tactical squads! having a tacitcal squad or two is helpfull for both numbers and battlefield options... your assault boyz do one thing: assault! but against say a numerically superior force like 'nids, guard or orks, it's helpfull to have some tactical marines nearby to lend some bolter fire to the cause!
golden rule #2; as pointed out, a chappy is pretty much mandetory to ensure your death company doesn't become a tactical liability!
golden rule #3; the combat squads rule really is a great thing! having more scoring units is always an advantage. being able to essentially double your starting number of scoring unit is rather damaging to your opponent's psychie as he/she is now forced to split their firepower even more...
the combat squads rule also makes things like the razorback a very viable option and it will help lessen the blow of scout squads becoming an elites choice... (ie: take a full 10-man scout squad, give half of them sniper rifles and now you can split them into both a shooty squad & an assaulty squad!)
golden rule #4; to get a furioso (reletively!) safely into the fray, give it a drop pod and support it with other deep striking troops and/or speedy units...
golden rule #5; always take a baal predator!
cheers!