This review is of the Early Access (pre-release) version of the game, current as of 10/13/2014, and pertains almost exclusively to the Survival mode of the game.
Early access it may be, but Space Engineers is worth a look if you enjoy builders (eg. Minecraft-style) games. I've spent much of the past weekend mining, refining, assembling, and then building the components of various ships and devices, to much enjoyment. Flight is Newtonian, jetpacks are standard, and the freedom of flight on top of the construction mechanics is enjoyable.
However, like most builder games, Space Engineers has a large element of resource collection and extraction. In this case, it's also part of the charm - there's nothing like building your first tunnel-boring machine and using it to core right through an enormous asteroid - but expect to spend some time mining if you're not simply playing creative mode. That means some relatively mundane mining - whether it's small scale mining by hand, or large scale resource extraction. It also means finding ores, but the game provides tools for this (ore detectors, lights, and conveyor/connector systems) to permit a player to facilitate this as much as possible mechanically without actually removing it.
When creating a survival mode world, give some consideration to your intended style of play. For instance, the game offers the opportunity to let welding (construction), grinding (deconstruction), refining (ores into ingots), assembly (ingots into components), and general inventory size be faster, more efficient, or simply larger. These changes can alter a survival mode game into something much more like the creative mode, or allow a single player to have the ability to move the ores and components of ten men when multiplayer is not available. None of this will stop a single player from playing as they wish, but it will have an impact on the level of tedium a player may have to ignore or overcome to enjoy the game.
Full disclosure: I'm currently playing a "all settings realistic" Lone Survivor start, where I've gotten my first mining barge up and running despite starting with nothing more than a hand drill and the basic machines needed to process ores and materials. There's a sense of satisfaction attached to starting with "nothing" and bootstrapping yourself into an effective spot.
As it's early access, the only "threat" the game proivides is in the form of wandering mostly-passive cargo vessels (turrets ahoy) to attack, scrap, or plunder (optional and default to off), or metor swarms hammering your landing pads and ships. Metors can be avoided easily by building some basic armor for your stations, or building them in the shadow of the rocks, but on the highest settings you'll be hard pressed to avoid the constant barrage of rock from above.
I'd recommend this - but keep in mind it's a lot like Minecraft. Sandbox and passive play is the order of the day, not frenetic action. (Though, the game certainly seems to support it, with gatling guns and rocket pods along with its assault rifles and jetpacks.) It's a much more spartan and simple affair than its learning curve will initially indicate, but there's plenty of sand from which to build your castle-in-the-sky.