As I said last time, I really think the new models are a bit of a disappointment. The new tanks are OK, but I won't be using them. The monstrosities that are centurions are as repulsive as they are overpriced, but they come with fairly craptastic rules, too. The new Tac squad is nice, but show me one Marine player that doesn't already have a few dozen tactical marines. These will sell simply because people will need the grav gun bits. What does all this add up to? Well the "model company" really didn't give people reasons to buy the new over-priced models. I look at the book and my old Ultramarines and I really don't see my army changing much. I wanted to add a squad of bikes for a while and the only change the new dex gave me was that those bikes will have 2 grav guns. This is a great place for a salvo weapon that does jack against horde since they keep the bike's bolters and can fire full effect on the move.
What it comes down to is an army that on the surface won't really change much. My list right now will stay largely the same. The new strengths of the army come from the tweaks that took place around that army. Aside from adding some grav guns, which if you're seeing lots of high armor units or monstrous creatures these are awesome, i don't see huge changes.
One group that I think really won here is the Black Templar. Yes, they lost their own codex, but they gained access to all the cool toys that other chapters have. They also have their own troop choice that can be min/maxed since it doesn't suffer from body-bag syndrome in any way.
Did the army improve? Absolutely, though in the interest of full disclosure, I was largely unimpressed with the 5th ed codex. Are they going to be the new uber army? I highly doubt it. What they're going to be good at is basically the same thing they always were...they're a tactically flexible army that can adapt, but isn't awesomely good at anything in particular. Their cc options are uninspiring, but were never amazing outside th/ss termies and in 6th that's not a problem. I'm playing Tau to prepare for Warstoreweekend, but after that I plan on dusting off the Second Company to see what they can do.