I recently came across a new (relatively new, came out 6 months ago) game on Steam called Space Engineers. It had some pretty good reviews (4.9 out of 5), and I watched a few trailers. A few people described it as "Minecraft For the advanced". I would describe it more as "Minecraft with advanced physics in space". While it is not very blocky, you do build a lot.
The game is in early access, which means that you can buy it for less ($25), but it will probably be unstable. The reason a developer would release a game before it is fully done is to get feedback so that a full release will appeal to the general public, and to get bugs fixed before (again) releasing to the general public. I have played it, and have not really come across any big (or even small) bugs.
The game has two modes, survival (not quite finished developing, but playable) and creative. In both modes, you can choose what kind of world you want. You can start on a plain platform, with a bit of fuel powering the oxygen and gravity generators. Or you can start on a platform with a large ship at your disposal, and a few small fighters and maintenance vehicles. The game, like Minecraft, has no end goal. In fact, you cannot even win the game, as you could in Minecraft (killing the Enderdragon). You build giant ships, small ships, station, and expand your space world with awesome creations. It has tons of features, like rotating pistons, hangar doors, motors, buttons, and more. You can build a space station, and have it send out mining drones that would find an asteroid, mine a bit, then come back and deposit the ores. You can also mass produce small ships, which can be sent out to explore the (optionally) infinite world.
Of course, all games will get boring if everything is left to you. However, not everything that happens depends on what you do. Random ships will spawn in the world and be sent in a random direction. Each ship has guns that will shoot you down if you get too near, but some have less guns then others. Sometimes, it will be a few ships, like a mining transport and a military escort. There isn't really a story behind the game, though some people like to roleplay. Each ship has some loot or other, and a few even have traps that will blow up the whole ship if you aren't careful. In survival, these ships are very useful as that can be broken down for their materials. In creative, it really fun to build a small ship and try blowing up as much as possible, while dodging the shots. The game is also multiplayer, which means you can do battles between you and your friends!
And if the game is to easy for you, or even if you want more of a challenge to your buildings, then you can turn on meteor showers. Depending on the setting, every few minutes randomly sized meteors will rain down causing considerable damage to you and your buildings. Unfortunately, they always come from the same direction, meaning that you can just build your space station on the other side of an asteroid and be safe.
And if it still isn't challenging or doesn't have enough features, it has a whole modding API! Some mods can add things like planets, or blocks, or just aesthetic features. Probably two of my favorite mods is one that makes the random ships that appear head towards you and attack you, and the other will spawn small ships at a random distance from you that have a small AI, which will try to do as much damage as possible to you. This means that adding guns to your base, even in creative mode, will actually become something you have to do to protect your buildings.
Overall, it is a really fun game, and I suggest you get it!