This game is really really fun. It has a long progression time, meaning you have LOTS of time before you reach end tier gameplay, which is awesome. As it is I think it is a very fun game...
However, and this isn't in my personal opinion enough to not recommend the game, the updates are really slow. New content is released in unstable builds quite regularly, but it's not necessarily "big" updates.
I took a break well over a half a year year ago since playing the game back when it first came out. When it first arrived the game was quite bland, with abusable bosses, and the only progression being "mine ore, fight boss, craft crafting bench, mine ore, fight boss, craft crafting bench, etc. etc.", although the atmosphere was (and still is) quite amazing.
Now in the new "big winter update" version, it's a heck of a lot better, with a ship you upgrade over time, an interesting active ability system, quests, dungeons, mini dungeons, and a fairly well paced progression system, among countless other fun things. I remember getting a good number of friends on my server with different instruments, and we all got together in a band and played a song, and it was pretty cool. There's a lot of possibilities to explore with what's provided.
For the building oriented players, I don't think it's quite on the level of games like terraria and minecraft, however the addition of wiring and futristic technology, along with lots of tile sets can allow for some pretty interesting building design. The game is certainly more combat oriented than it is building oriented.
I mean all in all, it's a pretty cool game, just keep in mind if you want a massive universe full of amazing discoveries and an MMO style experience, where you can run into other people on other planets, or if you want more than repeated structures and naturally generated terrain to find as you explore new planets, that's not in the game yet, and given the current pace, it's going to be a long long time before that goal is reached.
Recommendation: Skim a few youtube videos and watch a few trailers. If you think you'd like the game in it's current state, buy it now, have some good fun, and then put it off to the side for a while and come back later when it's more updated. It'll be the gift that keeps on giving. If you don't like it in it's current state, but like the planned features, you might have to wait a good while for those, but I would recommend you go through with that wait, since you never know what might happen to the development before those features arrive.