For those who haven't kept up with the development, the beta cycle is going to be in three phases. We're currently very close to the beginning of the first phase. As you should expect, things are very incomplete, some stuff doesn't work, there are tons of bugs, and your character will get wiped a lot.
That said, Steam reports that I've spent 21 glorious hours playing this game, and I could just keep going. Even this early, there's a lot of fun to be had. There are literally millions of planets...

It's surprisingly good even at the early stage... Steam has me clocked in at 78 hours. I haven't bothered to cheat, but I have wiped worlds after updates which resets all the ore and chests. They recommend the wipes to get the new balance adjustments to the worlds. I haven't been wiping my character (other than the one forced wipe so far), but I'm not using any of the over-powered weapons that happened one update.
The balance is definitely changing a lot, you notice every update. Especially the bosses, pre-wipe the first boss took me a long time to take down (and after he could destroy blocks he wiped out a large section of the world), but later he was much easier, ditto with the second. I'm just collecting pixels to trigger the 3rd boss (I have all the materials needed) so I'll get to see it for the first time, and I think the 4th boss is either in or going to be soon.
I really like just exploring and digging, then hopping to another planet. The universe is HUGE.
also, I really like those storage lockers also... I have a bunch in my ship :)