I had a bunch of friends buy it on Steam in the alpha, they said it was amazing and played in nonstop for about 2 weeks (maybe), then I never heard about it again. That typically means that the game is fun for about 5 minutes and has absolutely no replay value. So basically, the exact same as Terraria imo.
Nah, after piles of time with it, I can really say that's not quite the case.
Terraria's huge problem was that it was OBSESSED with the idea of progression. Your entire existence was focused on beating the big bosses. And with the small size of the game world, the game sorta forced you into that progression, because there were entire large areas of your world that you couldnt even enter until you were strong enough to keep from being 1-shotted.
And it didn't help that the combat became mindless after a time, due to the equipment gained by that progression being OP to the point of being ridiculous. Against later bosses, chances are you can fly, take next to no damage from attacks, heal instantly, cast super-long-range spells of horrible doom, swing a giant sword 2 times bigger than your character, and so on. There's ALOT of Metroid-ish powerups in the game, but they didn't balance the damn things out one bit, so once you have too many of them.... you are unstoppable. And because the game is so progression-focused, once you've DONE all of that.... suddenly, BAM, there's nothing else to really do. Sure you can make structures and all of that, but the game never really encourages it very well, due to the absolutely dirt-slow pace of the mining. Really tiny blocks combined with the ability to mine ONE block at a time, often very slowly, does not do good for the "build stuff" side of the game.
Starbound undoes alot of that, which is why my opinion of it is so high.
Buuuuuuuut, it has another problem: The developers. They're one of THOSE sorts, the really screwy ones whose actions dont always make a whole lot of sense, if any at all, and who dont know what a timetable is, or schedules, or similar things.
The game right now is still in a very unfinished state. It's got a long way to go, even despite the large amount of stuff in there already. There's alot of game mechanics still outright missing. But the devs.... ugh. They just make this part worse. Aside from the fact that the game's INITIAL release date was, what, 2 years ago I think? And then another failed date in 2013, well... yeah, they're still doing that. Back in February a decent sized patch comes out, fixing a few things, followed by the devs rambling about some very cool new features that were nearing completion. A short bit later, the patch is "delayed" because "yeah we've got a new office, gotta move into it!". And guess what the status is now? Still "working on the office", which I note was supposed to "really increase productivity once it's finished!", which.... yeah.
With the unfinished nature of the game, and the extreme impatience of players, AND the inherant lack of tolerance for early-access ANYTHING, people havent been as interested in it lately, so the game's population has dropped. It'll likely stay that way until they release another really major patch.
But yeah, they're that sort of dev. Which I might describe as being the polar-opposite of Arcen here.
They still know what they are doing, very definitely so, but they're absolutely dirt-freaking-slow, and not very good at all about feedback, and have LOTS of extremely random delays and things.