I've now put in 40 hours or so in a pretty small span of time. I've put 40 hours into Terraria as well and enjoy both games. I've also figured out how to run multiplayer pretty smoothly from my computer, so hit me up on Steam if you want someone to play with.
The progressions system is pretty grindy and seems a bit more straight forward and up front compared to Terraria, but in its current beta state you really need to use the wiki. I just beat the third boss which puts me in the fourth (out of ten) tiers. I'm grinding out some more armor and exploring the new sector.
The game seems pretty neat and open ended, but there is a lot of "make your own fun". For example, my friend and I found a village of bird people (all NPCs). It was a threat one planet so we could just wade through them taking their stuff and killing EVERYONE in sight. I found some cool items and we got some much needed resources.
We also found this platformer kind of dungeon that seemed a bit fun. It would probably be a real challenge with the floaty jumps etc. and seemed kind of cool. If any part is too hard you can just whip out your pick axe and tear it all apart and dig a hole to the end.
With the current beta I only have one more boss to go until I just grind up all the tiers to the end game - at that point there really won't be anything to do besides just building stuff and exploring.
So far, I'm loving it, but it's definitely still in its early stages and a bit of a stoner "feel good" game.
The monster designs look a bit too pokemon as well...