I'm really enjoying it. I just hit level 27 and I've been moving slowly through it. The one thing that really blows me away is the day/night/weather cycles in the game and how it can really effect come encounters. Dense and foggy, I start sniping enemies from a distance, move to my right and take cover while they blind fire at the location my shots came from. Enemies in the free roam areas level up as you do, while named boss encounters are at whatever level you currently are. Unlike Destiny where say the cosmodrome always has level 2-4 enemies when making planet fall.
A few things that I find annoying is how some enemies can nail you even if their weapon is both pointed at the ground and behind cover. Also, shotgunners from a great distance seem to be awfully accurate and do a huge amount of damage. I'm sure both will be patched at some point.
Either way, Great game!