That's the strength of Terraria. There is a hell of a lot of stuff there, but it's a game about discovery rather than construction. You're building a house pretty early on, of course, but that's just a base of operations. It's about going out and finding these things, because not only do they each come with their own little quirks, but the items you can get from these events and places are unique to those events and places. If you want Rocket Boots, you're going to have to pray for a goblin attack. If you want the space-age looking armour, you need a meteor to land somewhere.
Not only that, but you've got boss fights that happen when you hit the right activation point , each coming with their own attacks and weak spots, dropping their own unique loot. If you're bored, even for a second, you're really not playing the game right. It's not about a grind. It's about having a breather before the next amazing thing happens.
It's part of the weakness of Terraria, too. It can be overwhelming. There's so much going on all the time that if you don't know what half of it is, you're going to be at a loss. No one tells you that the zombies come out at night; you just have to stumble upon that one yourself. While there is a 'Guide' character that hovers around your house telling you little tips, he's only partially useful. The same goes for how the crafting works; if you have the materials to make something, it's listed when you're near the right crafting implement. If you don't have the right materials, or you're at the anvil, rather than the workbench, it won't show up.
So it's one of those games that you are going to need some outside help on. There are already exhaustive Wikis, detailing every nook and cranny of the game, allowing you to go it alone, using what other people have found as an almanac, leading you by the nose towards each discovery. But in that, something is lost. To have a game about discovery that needs other's discoveries to make it all hold together seems somewhat self-defeating. You're going to have to ration that readily-available knowledge to get the most out of the game, which is a shame.
Luckily, you don't have to play it alone. There's no real limit to how many people can join a server, only what that server can really handle. So you can adventure with your friend, having one of you hold the torch while the other digs away with their pickaxe. Or the one of you with a grappling hook can lay out a ladder for their partner, so you can both advance together. Or you can both fall down into the same chasm that neither of you saw and die together, cursing one another.
Your character persists through gameworlds, too, meaning that the demon axe you earned in one world can be taken to show off to your friends. Or you can invite their character into your world, to see that arboretum you built in the sky. Or the waterslide you created to get down to your mushroom farm in record time. Except you take away the water when they do it, so they get killed, and you laugh. Ha ha.
Minecraft's sandbox is the kind that comes with pristine sand and the best buckets and spades around. You've even got some mineral water on the side, so that you can wet it up and create some really fabulous looking crenelations. Terraria, on the other hand, is a sandbox where you can barely even see the sand for all the toys. It doesn't matter whether the fundamentals are all that brilliant, because of all these distractions. The cat might have used it as a litterbox once, but you can't tell what's between your toes because you're fighting a giant skeleton that's laughing at you while you fly around his head on rocket boots stabbing at him with a lightsaber.
There's one downside to all these toys, though, and that's that you'll get bored of them, eventually. After about twenty hours, you'll probably have a lot of the stuff you've been coveting for so long. And once you've got a character that can fly and kill pretty much anything it comes across, the impetus to explore and adventure is going to lessen somewhat. But this isn't a full-priced retail release, and it's priced accordingly. So twenty hours of fun is an impressive bit of value for money.
The other thing to note about all this is that Terraria isn't a static thing. The developers aren't just done with it now that it's out the door. In fact, the only reason it was released as it was is because a beta was leaked, so they all but rushed it out. It's been seeing hefty updates, adding new items and enemies, on top of refining the way the game works. It doesn't seem to be slowing down, either, meaning the game you can buy today wonít be the same game you can buy in six months time. So that twenty hours can easily turn into forty, sixty, a hundred. If you let it.
There's a reason Terraria has sold a few hundred thousand copies in the first few months it's been on sale. It's because, if Terraria really does have a bottom, no one can be bothered to go find it. They're having far too much fun on the surface, and the spaces in between.