Free floated barrel, so it will be more accurate than non-free floated (in theory). Although the gas piston harmonics are likely to throw off accuracy a bit compared to direct impingement.
Gas piston design IS better than direct impingement on a properly designed system. Less stoppages, and more reliable without lube in long term engagements. Keeps the hot gas out of the action, which is a good thing.
This is a good choice for the Marines. I'm glad to see that they are using their brains for once, instead of being stuck in the military rut, like the Army is. They are also issuing the new Gen 3 Magpul PMAG window as their new combat magazine, which is way better than the Army's enhanced GI mag, which isn't enhanced at all. Its a turd. The new Army GI mag is less reliable than the old GI mag.
As to the $3000 cost of current M4's, that's a far stretch. Those guns are about $500 to the GOVT. Including accessories, spare parts, ammo AND training, the cost could be calculated at $3000 per, but that's odd math.