With Str5+, rending, poison, AP2, multi-shot, weapons and monsters becoming more common in the game.. the once legendary 3+ power armor has actually turned into a liability.
This codex will be good if marines get a massive points reduction(which I think they will), and also a huge boost in fire power. I think the Chapter tactics will MAKE the army. If you asked me(2 years ago) if the new chapter tactics were over powered, based on the rumors I might've said yes. But now there is so much high power stuff in the game that T4 3+ save is almost useless, and you pay the points for it to boot. Also compared to other standard weapons, the bolter is a piece of junk.
So with points reduction with more buffs and MORE firepower, I think it will be a good codex.