On Earth you have three types of modes Story, Explore & Strike.
The story mission is quite short but gives you a bit of a background into what your role is in the game.
The Strike mission is very tough even with my level eight Titan & two other online players there were quite a few tough bosses to overcome. I died quite a few times on this but thankfully the co-op players were able to revive me.
The Explore mode is my favourite because it lets you explore the gorgeous terrain whilst completing simple missions and taking part in public events. I spent hours just exploring the many caves & underground passages. Occasionally you would come up against some very tough level 10+ enemies that you just could not harm. I found an opening in the dam wall which took me to an outside area littered with rusted vehicles.
Visually it looks amazing, I have some screenshots I took below & more on my PS4 which I will upload later.
Can't wait till July 17th for the Beta. I think I may have to take a couple of days off work to enjoy.